From c5f89fba55b2529b2c8a76e272a21d551ffa82fe Mon Sep 17 00:00:00 2001
From: Patrick Cloke <clokep@users.noreply.github.com>
Date: Mon, 30 Mar 2020 07:28:42 -0400
Subject: Add developer documentation for running a local CAS server (#7147)

---
 docs/dev/cas.md  | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 docs/dev/saml.md |  8 +++++--
 2 files changed, 70 insertions(+), 2 deletions(-)
 create mode 100644 docs/dev/cas.md

(limited to 'docs/dev')

diff --git a/docs/dev/cas.md b/docs/dev/cas.md
new file mode 100644
index 0000000000..f8d02cc82c
--- /dev/null
+++ b/docs/dev/cas.md
@@ -0,0 +1,64 @@
+# How to test CAS as a developer without a server
+
+The [django-mama-cas](https://github.com/jbittel/django-mama-cas) project is an
+easy to run CAS implementation built on top of Django.
+
+## Prerequisites
+
+1. Create a new virtualenv: `python3 -m venv <your virtualenv>`
+2. Activate your virtualenv: `source /path/to/your/virtualenv/bin/activate`
+3. Install Django and django-mama-cas:
+   ```
+   python -m pip install "django<3" "django-mama-cas==2.4.0"
+   ```
+4. Create a Django project in the current directory:
+   ```
+   django-admin startproject cas_test .
+   ```
+5. Follow the [install directions](https://django-mama-cas.readthedocs.io/en/latest/installation.html#configuring) for django-mama-cas
+6. Setup the SQLite database: `python manage.py migrate`
+7. Create a user:
+   ```
+   python manage.py createsuperuser
+   ```
+   1. Use whatever you want as the username and password.
+   2. Leave the other fields blank.
+8. Use the built-in Django test server to serve the CAS endpoints on port 8000:
+   ```
+   python manage.py runserver
+   ```
+
+You should now have a Django project configured to serve CAS authentication with
+a single user created.
+
+## Configure Synapse (and Riot) to use CAS
+
+1. Modify your `homeserver.yaml` to enable CAS and point it to your locally
+   running Django test server:
+   ```yaml
+   cas_config:
+     enabled: true
+     server_url: "http://localhost:8000"
+     service_url: "http://localhost:8081"
+     #displayname_attribute: name
+     #required_attributes:
+     #    name: value
+   ```
+2. Restart Synapse.
+
+Note that the above configuration assumes the homeserver is running on port 8081
+and that the CAS server is on port 8000, both on localhost.
+
+## Testing the configuration
+
+Then in Riot:
+
+1. Visit the login page with a Riot pointing at your homeserver.
+2. Click the Single Sign-On button.
+3. Login using the credentials created with `createsuperuser`.
+4. You should be logged in.
+
+If you want to repeat this process you'll need to manually logout first:
+
+1. http://localhost:8000/admin/
+2. Click "logout" in the top right.
diff --git a/docs/dev/saml.md b/docs/dev/saml.md
index f41aadce47..a9bfd2dc05 100644
--- a/docs/dev/saml.md
+++ b/docs/dev/saml.md
@@ -18,9 +18,13 @@ To make Synapse (and therefore Riot) use it:
        metadata:
          local: ["samling.xml"]   
    ```
-5. Run `apt-get install xmlsec1` and `pip install --upgrade --force 'pysaml2>=4.5.0'` to ensure
+5. Ensure that your `homeserver.yaml` has a setting for `public_baseurl`:
+   ```yaml
+   public_baseurl: http://localhost:8080/
+   ```
+6. Run `apt-get install xmlsec1` and `pip install --upgrade --force 'pysaml2>=4.5.0'` to ensure
    the dependencies are installed and ready to go.
-6. Restart Synapse.
+7. Restart Synapse.
 
 Then in Riot:
 
-- 
cgit 1.5.1


From 616af44137c78d481024da83bb51ed0d50a49522 Mon Sep 17 00:00:00 2001
From: Quentin Gliech <quentingliech@gmail.com>
Date: Fri, 8 May 2020 14:30:40 +0200
Subject: Implement OpenID Connect-based login (#7256)

---
 changelog.d/7256.feature               |   1 +
 docs/dev/oidc.md                       | 175 ++++++
 docs/sample_config.yaml                |  95 ++++
 mypy.ini                               |   3 +
 synapse/app/homeserver.py              |  12 +
 synapse/config/_base.pyi               |   2 +
 synapse/config/homeserver.py           |   2 +
 synapse/config/oidc_config.py          | 177 ++++++
 synapse/config/sso.py                  |  17 +-
 synapse/handlers/auth.py               |   4 +-
 synapse/handlers/oidc_handler.py       | 998 +++++++++++++++++++++++++++++++++
 synapse/http/client.py                 |   7 +
 synapse/python_dependencies.py         |   1 +
 synapse/res/templates/sso_error.html   |  18 +
 synapse/rest/client/v1/login.py        |  28 +-
 synapse/rest/oidc/__init__.py          |  27 +
 synapse/rest/oidc/callback_resource.py |  31 +
 synapse/server.py                      |   6 +
 synapse/server.pyi                     |   5 +
 tests/handlers/test_oidc.py            | 565 +++++++++++++++++++
 tox.ini                                |   1 +
 21 files changed, 2163 insertions(+), 12 deletions(-)
 create mode 100644 changelog.d/7256.feature
 create mode 100644 docs/dev/oidc.md
 create mode 100644 synapse/config/oidc_config.py
 create mode 100644 synapse/handlers/oidc_handler.py
 create mode 100644 synapse/res/templates/sso_error.html
 create mode 100644 synapse/rest/oidc/__init__.py
 create mode 100644 synapse/rest/oidc/callback_resource.py
 create mode 100644 tests/handlers/test_oidc.py

(limited to 'docs/dev')

diff --git a/changelog.d/7256.feature b/changelog.d/7256.feature
new file mode 100644
index 0000000000..7ad767bf71
--- /dev/null
+++ b/changelog.d/7256.feature
@@ -0,0 +1 @@
+Add OpenID Connect login/registration support. Contributed by Quentin Gliech, on behalf of [les Connecteurs](https://connecteu.rs).
diff --git a/docs/dev/oidc.md b/docs/dev/oidc.md
new file mode 100644
index 0000000000..a90c5d2441
--- /dev/null
+++ b/docs/dev/oidc.md
@@ -0,0 +1,175 @@
+# How to test OpenID Connect
+
+Any OpenID Connect Provider (OP) should work with Synapse, as long as it supports the authorization code flow.
+There are a few options for that:
+
+ - start a local OP. Synapse has been tested with [Hydra][hydra] and [Dex][dex-idp].
+   Note that for an OP to work, it should be served under a secure (HTTPS) origin.
+   A certificate signed with a self-signed, locally trusted CA should work. In that case, start Synapse with a `SSL_CERT_FILE` environment variable set to the path of the CA.
+ - use a publicly available OP. Synapse has been tested with [Google][google-idp].
+ - setup a SaaS OP, like [Auth0][auth0] and [Okta][okta]. Auth0 has a free tier which has been tested with Synapse.
+
+[google-idp]: https://developers.google.com/identity/protocols/OpenIDConnect#authenticatingtheuser
+[auth0]: https://auth0.com/
+[okta]: https://www.okta.com/
+[dex-idp]: https://github.com/dexidp/dex
+[hydra]: https://www.ory.sh/docs/hydra/
+
+
+## Sample configs
+
+Here are a few configs for providers that should work with Synapse.
+
+### [Dex][dex-idp]
+
+[Dex][dex-idp] is a simple, open-source, certified OpenID Connect Provider.
+Although it is designed to help building a full-blown provider, with some external database, it can be configured with static passwords in a config file.
+
+Follow the [Getting Started guide](https://github.com/dexidp/dex/blob/master/Documentation/getting-started.md) to install Dex.
+
+Edit `examples/config-dev.yaml` config file from the Dex repo to add a client:
+
+```yaml
+staticClients:
+- id: synapse
+  secret: secret
+  redirectURIs:
+  - '[synapse base url]/_synapse/oidc/callback'
+  name: 'Synapse'
+```
+
+Run with `dex serve examples/config-dex.yaml`
+
+Synapse config:
+
+```yaml
+oidc_config:
+   enabled: true
+   skip_verification: true # This is needed as Dex is served on an insecure endpoint
+   issuer: "http://127.0.0.1:5556/dex"
+   discover: true
+   client_id: "synapse"
+   client_secret: "secret"
+   scopes:
+     - openid
+     - profile
+   user_mapping_provider:
+     config:
+       localpart_template: '{{ user.name }}'
+       display_name_template: '{{ user.name|capitalize }}'
+```
+
+### [Auth0][auth0]
+
+1. Create a regular web application for Synapse
+2. Set the Allowed Callback URLs to `[synapse base url]/_synapse/oidc/callback`
+3. Add a rule to add the `preferred_username` claim.
+   <details>
+    <summary>Code sample</summary>
+
+    ```js
+    function addPersistenceAttribute(user, context, callback) {
+      user.user_metadata = user.user_metadata || {};
+      user.user_metadata.preferred_username = user.user_metadata.preferred_username || user.user_id;
+      context.idToken.preferred_username = user.user_metadata.preferred_username;
+
+      auth0.users.updateUserMetadata(user.user_id, user.user_metadata)
+        .then(function(){
+            callback(null, user, context);
+        })
+        .catch(function(err){
+            callback(err);
+        });
+    }
+    ```
+
+  </details>
+
+
+```yaml
+oidc_config:
+   enabled: true
+   issuer: "https://your-tier.eu.auth0.com/" # TO BE FILLED
+   discover: true
+   client_id: "your-client-id" # TO BE FILLED
+   client_secret: "your-client-secret" # TO BE FILLED
+   scopes:
+     - openid
+     - profile
+   user_mapping_provider:
+     config:
+       localpart_template: '{{ user.preferred_username }}'
+       display_name_template: '{{ user.name }}'
+```
+
+### GitHub
+
+GitHub is a bit special as it is not an OpenID Connect compliant provider, but just a regular OAuth2 provider.
+The `/user` API endpoint can be used to retrieve informations from the user.
+As the OIDC login mechanism needs an attribute to uniquely identify users and that endpoint does not return a `sub` property, an alternative `subject_claim` has to be set.
+
+1. Create a new OAuth application: https://github.com/settings/applications/new
+2. Set the callback URL to `[synapse base url]/_synapse/oidc/callback`
+
+```yaml
+oidc_config:
+   enabled: true
+   issuer: "https://github.com/"
+   discover: false
+   client_id: "your-client-id" # TO BE FILLED
+   client_secret: "your-client-secret" # TO BE FILLED
+   authorization_endpoint: "https://github.com/login/oauth/authorize"
+   token_endpoint: "https://github.com/login/oauth/access_token"
+   userinfo_endpoint: "https://api.github.com/user"
+   scopes:
+     - read:user
+   user_mapping_provider:
+     config:
+       subject_claim: 'id'
+       localpart_template: '{{ user.login }}'
+       display_name_template: '{{ user.name }}'
+```
+
+### Google
+
+1. Setup a project in the Google API Console
+2. Obtain the OAuth 2.0 credentials (see <https://developers.google.com/identity/protocols/oauth2/openid-connect>)
+3. Add this Authorized redirect URI: `[synapse base url]/_synapse/oidc/callback`
+
+```yaml
+oidc_config:
+   enabled: true
+   issuer: "https://accounts.google.com/"
+   discover: true
+   client_id: "your-client-id" # TO BE FILLED
+   client_secret: "your-client-secret" # TO BE FILLED
+   scopes:
+     - openid
+     - profile
+   user_mapping_provider:
+     config:
+       localpart_template: '{{ user.given_name|lower }}'
+       display_name_template: '{{ user.name }}'
+```
+
+### Twitch
+
+1. Setup a developer account on [Twitch](https://dev.twitch.tv/)
+2. Obtain the OAuth 2.0 credentials by [creating an app](https://dev.twitch.tv/console/apps/)
+3. Add this OAuth Redirect URL: `[synapse base url]/_synapse/oidc/callback`
+
+```yaml
+oidc_config:
+   enabled: true
+   issuer: "https://id.twitch.tv/oauth2/"
+   discover: true
+   client_id: "your-client-id" # TO BE FILLED
+   client_secret: "your-client-secret" # TO BE FILLED
+   client_auth_method: "client_secret_post"
+   scopes:
+     - openid
+   user_mapping_provider:
+     config:
+       localpart_template: '{{ user.preferred_username }}'
+       display_name_template: '{{ user.name }}'
+```
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index 98ead7dc0e..1e397f7734 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -1470,6 +1470,94 @@ saml2_config:
   #template_dir: "res/templates"
 
 
+# Enable OpenID Connect for registration and login. Uses authlib.
+#
+oidc_config:
+    # enable OpenID Connect. Defaults to false.
+    #
+    #enabled: true
+
+    # use the OIDC discovery mechanism to discover endpoints. Defaults to true.
+    #
+    #discover: true
+
+    # the OIDC issuer. Used to validate tokens and discover the providers endpoints. Required.
+    #
+    #issuer: "https://accounts.example.com/"
+
+    # oauth2 client id to use. Required.
+    #
+    #client_id: "provided-by-your-issuer"
+
+    # oauth2 client secret to use. Required.
+    #
+    #client_secret: "provided-by-your-issuer"
+
+    # auth method to use when exchanging the token.
+    # Valid values are "client_secret_basic" (default), "client_secret_post" and "none".
+    #
+    #client_auth_method: "client_auth_basic"
+
+    # list of scopes to ask. This should include the "openid" scope. Defaults to ["openid"].
+    #
+    #scopes: ["openid"]
+
+    # the oauth2 authorization endpoint. Required if provider discovery is disabled.
+    #
+    #authorization_endpoint: "https://accounts.example.com/oauth2/auth"
+
+    # the oauth2 token endpoint. Required if provider discovery is disabled.
+    #
+    #token_endpoint: "https://accounts.example.com/oauth2/token"
+
+    # the OIDC userinfo endpoint. Required if discovery is disabled and the "openid" scope is not asked.
+    #
+    #userinfo_endpoint: "https://accounts.example.com/userinfo"
+
+    # URI where to fetch the JWKS. Required if discovery is disabled and the "openid" scope is used.
+    #
+    #jwks_uri: "https://accounts.example.com/.well-known/jwks.json"
+
+    # skip metadata verification. Defaults to false.
+    # Use this if you are connecting to a provider that is not OpenID Connect compliant.
+    # Avoid this in production.
+    #
+    #skip_verification: false
+
+
+    # An external module can be provided here as a custom solution to mapping
+    # attributes returned from a OIDC provider onto a matrix user.
+    #
+    user_mapping_provider:
+      # The custom module's class. Uncomment to use a custom module.
+      # Default is 'synapse.handlers.oidc_handler.JinjaOidcMappingProvider'.
+      #
+      #module: mapping_provider.OidcMappingProvider
+
+      # Custom configuration values for the module. Below options are intended
+      # for the built-in provider, they should be changed if using a custom
+      # module. This section will be passed as a Python dictionary to the
+      # module's `parse_config` method.
+      #
+      # Below is the config of the default mapping provider, based on Jinja2
+      # templates. Those templates are used to render user attributes, where the
+      # userinfo object is available through the `user` variable.
+      #
+      config:
+        # name of the claim containing a unique identifier for the user.
+        # Defaults to `sub`, which OpenID Connect compliant providers should provide.
+        #
+        #subject_claim: "sub"
+
+        # Jinja2 template for the localpart of the MXID
+        #
+        localpart_template: "{{ user.preferred_username }}"
+
+        # Jinja2 template for the display name to set on first login. Optional.
+        #
+        #display_name_template: "{{ user.given_name }} {{ user.last_name }}"
+
+
 
 # Enable CAS for registration and login.
 #
@@ -1554,6 +1642,13 @@ sso:
     #
     #   This template has no additional variables.
     #
+    # * HTML page to display to users if something goes wrong during the
+    #   OpenID Connect authentication process: 'sso_error.html'.
+    #
+    #   When rendering, this template is given two variables:
+    #     * error: the technical name of the error
+    #     * error_description: a human-readable message for the error
+    #
     # You can see the default templates at:
     # https://github.com/matrix-org/synapse/tree/master/synapse/res/templates
     #
diff --git a/mypy.ini b/mypy.ini
index 69be2f67ad..3533797d68 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -75,3 +75,6 @@ ignore_missing_imports = True
 
 [mypy-jwt.*]
 ignore_missing_imports = True
+
+[mypy-authlib.*]
+ignore_missing_imports = True
diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index cbd1ea475a..bc8695d8dd 100644
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -192,6 +192,11 @@ class SynapseHomeServer(HomeServer):
                 }
             )
 
+            if self.get_config().oidc_enabled:
+                from synapse.rest.oidc import OIDCResource
+
+                resources["/_synapse/oidc"] = OIDCResource(self)
+
             if self.get_config().saml2_enabled:
                 from synapse.rest.saml2 import SAML2Resource
 
@@ -422,6 +427,13 @@ def setup(config_options):
                 # Check if it needs to be reprovisioned every day.
                 hs.get_clock().looping_call(reprovision_acme, 24 * 60 * 60 * 1000)
 
+            # Load the OIDC provider metadatas, if OIDC is enabled.
+            if hs.config.oidc_enabled:
+                oidc = hs.get_oidc_handler()
+                # Loading the provider metadata also ensures the provider config is valid.
+                yield defer.ensureDeferred(oidc.load_metadata())
+                yield defer.ensureDeferred(oidc.load_jwks())
+
             _base.start(hs, config.listeners)
 
             hs.get_datastore().db.updates.start_doing_background_updates()
diff --git a/synapse/config/_base.pyi b/synapse/config/_base.pyi
index 3053fc9d27..9e576060d4 100644
--- a/synapse/config/_base.pyi
+++ b/synapse/config/_base.pyi
@@ -13,6 +13,7 @@ from synapse.config import (
     key,
     logger,
     metrics,
+    oidc_config,
     password,
     password_auth_providers,
     push,
@@ -59,6 +60,7 @@ class RootConfig:
     saml2: saml2_config.SAML2Config
     cas: cas.CasConfig
     sso: sso.SSOConfig
+    oidc: oidc_config.OIDCConfig
     jwt: jwt_config.JWTConfig
     password: password.PasswordConfig
     email: emailconfig.EmailConfig
diff --git a/synapse/config/homeserver.py b/synapse/config/homeserver.py
index be6c6afa74..996d3e6bf7 100644
--- a/synapse/config/homeserver.py
+++ b/synapse/config/homeserver.py
@@ -27,6 +27,7 @@ from .jwt_config import JWTConfig
 from .key import KeyConfig
 from .logger import LoggingConfig
 from .metrics import MetricsConfig
+from .oidc_config import OIDCConfig
 from .password import PasswordConfig
 from .password_auth_providers import PasswordAuthProviderConfig
 from .push import PushConfig
@@ -66,6 +67,7 @@ class HomeServerConfig(RootConfig):
         AppServiceConfig,
         KeyConfig,
         SAML2Config,
+        OIDCConfig,
         CasConfig,
         SSOConfig,
         JWTConfig,
diff --git a/synapse/config/oidc_config.py b/synapse/config/oidc_config.py
new file mode 100644
index 0000000000..5af110745e
--- /dev/null
+++ b/synapse/config/oidc_config.py
@@ -0,0 +1,177 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Quentin Gliech
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.python_dependencies import DependencyException, check_requirements
+from synapse.util.module_loader import load_module
+
+from ._base import Config, ConfigError
+
+DEFAULT_USER_MAPPING_PROVIDER = "synapse.handlers.oidc_handler.JinjaOidcMappingProvider"
+
+
+class OIDCConfig(Config):
+    section = "oidc"
+
+    def read_config(self, config, **kwargs):
+        self.oidc_enabled = False
+
+        oidc_config = config.get("oidc_config")
+
+        if not oidc_config or not oidc_config.get("enabled", False):
+            return
+
+        try:
+            check_requirements("oidc")
+        except DependencyException as e:
+            raise ConfigError(e.message)
+
+        public_baseurl = self.public_baseurl
+        if public_baseurl is None:
+            raise ConfigError("oidc_config requires a public_baseurl to be set")
+        self.oidc_callback_url = public_baseurl + "_synapse/oidc/callback"
+
+        self.oidc_enabled = True
+        self.oidc_discover = oidc_config.get("discover", True)
+        self.oidc_issuer = oidc_config["issuer"]
+        self.oidc_client_id = oidc_config["client_id"]
+        self.oidc_client_secret = oidc_config["client_secret"]
+        self.oidc_client_auth_method = oidc_config.get(
+            "client_auth_method", "client_secret_basic"
+        )
+        self.oidc_scopes = oidc_config.get("scopes", ["openid"])
+        self.oidc_authorization_endpoint = oidc_config.get("authorization_endpoint")
+        self.oidc_token_endpoint = oidc_config.get("token_endpoint")
+        self.oidc_userinfo_endpoint = oidc_config.get("userinfo_endpoint")
+        self.oidc_jwks_uri = oidc_config.get("jwks_uri")
+        self.oidc_subject_claim = oidc_config.get("subject_claim", "sub")
+        self.oidc_skip_verification = oidc_config.get("skip_verification", False)
+
+        ump_config = oidc_config.get("user_mapping_provider", {})
+        ump_config.setdefault("module", DEFAULT_USER_MAPPING_PROVIDER)
+        ump_config.setdefault("config", {})
+
+        (
+            self.oidc_user_mapping_provider_class,
+            self.oidc_user_mapping_provider_config,
+        ) = load_module(ump_config)
+
+        # Ensure loaded user mapping module has defined all necessary methods
+        required_methods = [
+            "get_remote_user_id",
+            "map_user_attributes",
+        ]
+        missing_methods = [
+            method
+            for method in required_methods
+            if not hasattr(self.oidc_user_mapping_provider_class, method)
+        ]
+        if missing_methods:
+            raise ConfigError(
+                "Class specified by oidc_config."
+                "user_mapping_provider.module is missing required "
+                "methods: %s" % (", ".join(missing_methods),)
+            )
+
+    def generate_config_section(self, config_dir_path, server_name, **kwargs):
+        return """\
+        # Enable OpenID Connect for registration and login. Uses authlib.
+        #
+        oidc_config:
+            # enable OpenID Connect. Defaults to false.
+            #
+            #enabled: true
+
+            # use the OIDC discovery mechanism to discover endpoints. Defaults to true.
+            #
+            #discover: true
+
+            # the OIDC issuer. Used to validate tokens and discover the providers endpoints. Required.
+            #
+            #issuer: "https://accounts.example.com/"
+
+            # oauth2 client id to use. Required.
+            #
+            #client_id: "provided-by-your-issuer"
+
+            # oauth2 client secret to use. Required.
+            #
+            #client_secret: "provided-by-your-issuer"
+
+            # auth method to use when exchanging the token.
+            # Valid values are "client_secret_basic" (default), "client_secret_post" and "none".
+            #
+            #client_auth_method: "client_auth_basic"
+
+            # list of scopes to ask. This should include the "openid" scope. Defaults to ["openid"].
+            #
+            #scopes: ["openid"]
+
+            # the oauth2 authorization endpoint. Required if provider discovery is disabled.
+            #
+            #authorization_endpoint: "https://accounts.example.com/oauth2/auth"
+
+            # the oauth2 token endpoint. Required if provider discovery is disabled.
+            #
+            #token_endpoint: "https://accounts.example.com/oauth2/token"
+
+            # the OIDC userinfo endpoint. Required if discovery is disabled and the "openid" scope is not asked.
+            #
+            #userinfo_endpoint: "https://accounts.example.com/userinfo"
+
+            # URI where to fetch the JWKS. Required if discovery is disabled and the "openid" scope is used.
+            #
+            #jwks_uri: "https://accounts.example.com/.well-known/jwks.json"
+
+            # skip metadata verification. Defaults to false.
+            # Use this if you are connecting to a provider that is not OpenID Connect compliant.
+            # Avoid this in production.
+            #
+            #skip_verification: false
+
+
+            # An external module can be provided here as a custom solution to mapping
+            # attributes returned from a OIDC provider onto a matrix user.
+            #
+            user_mapping_provider:
+              # The custom module's class. Uncomment to use a custom module.
+              # Default is {mapping_provider!r}.
+              #
+              #module: mapping_provider.OidcMappingProvider
+
+              # Custom configuration values for the module. Below options are intended
+              # for the built-in provider, they should be changed if using a custom
+              # module. This section will be passed as a Python dictionary to the
+              # module's `parse_config` method.
+              #
+              # Below is the config of the default mapping provider, based on Jinja2
+              # templates. Those templates are used to render user attributes, where the
+              # userinfo object is available through the `user` variable.
+              #
+              config:
+                # name of the claim containing a unique identifier for the user.
+                # Defaults to `sub`, which OpenID Connect compliant providers should provide.
+                #
+                #subject_claim: "sub"
+
+                # Jinja2 template for the localpart of the MXID
+                #
+                localpart_template: "{{{{ user.preferred_username }}}}"
+
+                # Jinja2 template for the display name to set on first login. Optional.
+                #
+                #display_name_template: "{{{{ user.given_name }}}} {{{{ user.last_name }}}}"
+        """.format(
+            mapping_provider=DEFAULT_USER_MAPPING_PROVIDER
+        )
diff --git a/synapse/config/sso.py b/synapse/config/sso.py
index cac6bc0139..aff642f015 100644
--- a/synapse/config/sso.py
+++ b/synapse/config/sso.py
@@ -36,17 +36,13 @@ class SSOConfig(Config):
         if not template_dir:
             template_dir = pkg_resources.resource_filename("synapse", "res/templates",)
 
-        self.sso_redirect_confirm_template_dir = template_dir
+        self.sso_template_dir = template_dir
         self.sso_account_deactivated_template = self.read_file(
-            os.path.join(
-                self.sso_redirect_confirm_template_dir, "sso_account_deactivated.html"
-            ),
+            os.path.join(self.sso_template_dir, "sso_account_deactivated.html"),
             "sso_account_deactivated_template",
         )
         self.sso_auth_success_template = self.read_file(
-            os.path.join(
-                self.sso_redirect_confirm_template_dir, "sso_auth_success.html"
-            ),
+            os.path.join(self.sso_template_dir, "sso_auth_success.html"),
             "sso_auth_success_template",
         )
 
@@ -137,6 +133,13 @@ class SSOConfig(Config):
             #
             #   This template has no additional variables.
             #
+            # * HTML page to display to users if something goes wrong during the
+            #   OpenID Connect authentication process: 'sso_error.html'.
+            #
+            #   When rendering, this template is given two variables:
+            #     * error: the technical name of the error
+            #     * error_description: a human-readable message for the error
+            #
             # You can see the default templates at:
             # https://github.com/matrix-org/synapse/tree/master/synapse/res/templates
             #
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index 7613e5b6ab..f8d2331bf1 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -126,13 +126,13 @@ class AuthHandler(BaseHandler):
         # It notifies the user they are about to give access to their matrix account
         # to the client.
         self._sso_redirect_confirm_template = load_jinja2_templates(
-            hs.config.sso_redirect_confirm_template_dir, ["sso_redirect_confirm.html"],
+            hs.config.sso_template_dir, ["sso_redirect_confirm.html"],
         )[0]
         # The following template is shown during user interactive authentication
         # in the fallback auth scenario. It notifies the user that they are
         # authenticating for an operation to occur on their account.
         self._sso_auth_confirm_template = load_jinja2_templates(
-            hs.config.sso_redirect_confirm_template_dir, ["sso_auth_confirm.html"],
+            hs.config.sso_template_dir, ["sso_auth_confirm.html"],
         )[0]
         # The following template is shown after a successful user interactive
         # authentication session. It tells the user they can close the window.
diff --git a/synapse/handlers/oidc_handler.py b/synapse/handlers/oidc_handler.py
new file mode 100644
index 0000000000..178f263439
--- /dev/null
+++ b/synapse/handlers/oidc_handler.py
@@ -0,0 +1,998 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Quentin Gliech
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import json
+import logging
+from typing import Dict, Generic, List, Optional, Tuple, TypeVar
+from urllib.parse import urlencode
+
+import attr
+import pymacaroons
+from authlib.common.security import generate_token
+from authlib.jose import JsonWebToken
+from authlib.oauth2.auth import ClientAuth
+from authlib.oauth2.rfc6749.parameters import prepare_grant_uri
+from authlib.oidc.core import CodeIDToken, ImplicitIDToken, UserInfo
+from authlib.oidc.discovery import OpenIDProviderMetadata, get_well_known_url
+from jinja2 import Environment, Template
+from pymacaroons.exceptions import (
+    MacaroonDeserializationException,
+    MacaroonInvalidSignatureException,
+)
+from typing_extensions import TypedDict
+
+from twisted.web.client import readBody
+
+from synapse.config import ConfigError
+from synapse.http.server import finish_request
+from synapse.http.site import SynapseRequest
+from synapse.push.mailer import load_jinja2_templates
+from synapse.server import HomeServer
+from synapse.types import UserID, map_username_to_mxid_localpart
+
+logger = logging.getLogger(__name__)
+
+SESSION_COOKIE_NAME = b"oidc_session"
+
+#: A token exchanged from the token endpoint, as per RFC6749 sec 5.1. and
+#: OpenID.Core sec 3.1.3.3.
+Token = TypedDict(
+    "Token",
+    {
+        "access_token": str,
+        "token_type": str,
+        "id_token": Optional[str],
+        "refresh_token": Optional[str],
+        "expires_in": int,
+        "scope": Optional[str],
+    },
+)
+
+#: A JWK, as per RFC7517 sec 4. The type could be more precise than that, but
+#: there is no real point of doing this in our case.
+JWK = Dict[str, str]
+
+#: A JWK Set, as per RFC7517 sec 5.
+JWKS = TypedDict("JWKS", {"keys": List[JWK]})
+
+
+class OidcError(Exception):
+    """Used to catch errors when calling the token_endpoint
+    """
+
+    def __init__(self, error, error_description=None):
+        self.error = error
+        self.error_description = error_description
+
+    def __str__(self):
+        if self.error_description:
+            return "{}: {}".format(self.error, self.error_description)
+        return self.error
+
+
+class MappingException(Exception):
+    """Used to catch errors when mapping the UserInfo object
+    """
+
+
+class OidcHandler:
+    """Handles requests related to the OpenID Connect login flow.
+    """
+
+    def __init__(self, hs: HomeServer):
+        self._callback_url = hs.config.oidc_callback_url  # type: str
+        self._scopes = hs.config.oidc_scopes  # type: List[str]
+        self._client_auth = ClientAuth(
+            hs.config.oidc_client_id,
+            hs.config.oidc_client_secret,
+            hs.config.oidc_client_auth_method,
+        )  # type: ClientAuth
+        self._client_auth_method = hs.config.oidc_client_auth_method  # type: str
+        self._subject_claim = hs.config.oidc_subject_claim
+        self._provider_metadata = OpenIDProviderMetadata(
+            issuer=hs.config.oidc_issuer,
+            authorization_endpoint=hs.config.oidc_authorization_endpoint,
+            token_endpoint=hs.config.oidc_token_endpoint,
+            userinfo_endpoint=hs.config.oidc_userinfo_endpoint,
+            jwks_uri=hs.config.oidc_jwks_uri,
+        )  # type: OpenIDProviderMetadata
+        self._provider_needs_discovery = hs.config.oidc_discover  # type: bool
+        self._user_mapping_provider = hs.config.oidc_user_mapping_provider_class(
+            hs.config.oidc_user_mapping_provider_config
+        )  # type: OidcMappingProvider
+        self._skip_verification = hs.config.oidc_skip_verification  # type: bool
+
+        self._http_client = hs.get_proxied_http_client()
+        self._auth_handler = hs.get_auth_handler()
+        self._registration_handler = hs.get_registration_handler()
+        self._datastore = hs.get_datastore()
+        self._clock = hs.get_clock()
+        self._hostname = hs.hostname  # type: str
+        self._server_name = hs.config.server_name  # type: str
+        self._macaroon_secret_key = hs.config.macaroon_secret_key
+        self._error_template = load_jinja2_templates(
+            hs.config.sso_template_dir, ["sso_error.html"]
+        )[0]
+
+        # identifier for the external_ids table
+        self._auth_provider_id = "oidc"
+
+    def _render_error(
+        self, request, error: str, error_description: Optional[str] = None
+    ) -> None:
+        """Renders the error template and respond with it.
+
+        This is used to show errors to the user. The template of this page can
+        be found under ``synapse/res/templates/sso_error.html``.
+
+        Args:
+            request: The incoming request from the browser.
+                We'll respond with an HTML page describing the error.
+            error: A technical identifier for this error. Those include
+                well-known OAuth2/OIDC error types like invalid_request or
+                access_denied.
+            error_description: A human-readable description of the error.
+        """
+        html_bytes = self._error_template.render(
+            error=error, error_description=error_description
+        ).encode("utf-8")
+
+        request.setResponseCode(400)
+        request.setHeader(b"Content-Type", b"text/html; charset=utf-8")
+        request.setHeader(b"Content-Length", b"%i" % len(html_bytes))
+        request.write(html_bytes)
+        finish_request(request)
+
+    def _validate_metadata(self):
+        """Verifies the provider metadata.
+
+        This checks the validity of the currently loaded provider. Not
+        everything is checked, only:
+
+          - ``issuer``
+          - ``authorization_endpoint``
+          - ``token_endpoint``
+          - ``response_types_supported`` (checks if "code" is in it)
+          - ``jwks_uri``
+
+        Raises:
+            ValueError: if something in the provider is not valid
+        """
+        # Skip verification to allow non-compliant providers (e.g. issuers not running on a secure origin)
+        if self._skip_verification is True:
+            return
+
+        m = self._provider_metadata
+        m.validate_issuer()
+        m.validate_authorization_endpoint()
+        m.validate_token_endpoint()
+
+        if m.get("token_endpoint_auth_methods_supported") is not None:
+            m.validate_token_endpoint_auth_methods_supported()
+            if (
+                self._client_auth_method
+                not in m["token_endpoint_auth_methods_supported"]
+            ):
+                raise ValueError(
+                    '"{auth_method}" not in "token_endpoint_auth_methods_supported" ({supported!r})'.format(
+                        auth_method=self._client_auth_method,
+                        supported=m["token_endpoint_auth_methods_supported"],
+                    )
+                )
+
+        if m.get("response_types_supported") is not None:
+            m.validate_response_types_supported()
+
+            if "code" not in m["response_types_supported"]:
+                raise ValueError(
+                    '"code" not in "response_types_supported" (%r)'
+                    % (m["response_types_supported"],)
+                )
+
+        # If the openid scope was not requested, we need a userinfo endpoint to fetch user infos
+        if self._uses_userinfo:
+            if m.get("userinfo_endpoint") is None:
+                raise ValueError(
+                    'provider has no "userinfo_endpoint", even though it is required because the "openid" scope is not requested'
+                )
+        else:
+            # If we're not using userinfo, we need a valid jwks to validate the ID token
+            if m.get("jwks") is None:
+                if m.get("jwks_uri") is not None:
+                    m.validate_jwks_uri()
+                else:
+                    raise ValueError('"jwks_uri" must be set')
+
+    @property
+    def _uses_userinfo(self) -> bool:
+        """Returns True if the ``userinfo_endpoint`` should be used.
+
+        This is based on the requested scopes: if the scopes include
+        ``openid``, the provider should give use an ID token containing the
+        user informations. If not, we should fetch them using the
+        ``access_token`` with the ``userinfo_endpoint``.
+        """
+
+        # Maybe that should be user-configurable and not inferred?
+        return "openid" not in self._scopes
+
+    async def load_metadata(self) -> OpenIDProviderMetadata:
+        """Load and validate the provider metadata.
+
+        The values metadatas are discovered if ``oidc_config.discovery`` is
+        ``True`` and then cached.
+
+        Raises:
+            ValueError: if something in the provider is not valid
+
+        Returns:
+            The provider's metadata.
+        """
+        # If we are using the OpenID Discovery documents, it needs to be loaded once
+        # FIXME: should there be a lock here?
+        if self._provider_needs_discovery:
+            url = get_well_known_url(self._provider_metadata["issuer"], external=True)
+            metadata_response = await self._http_client.get_json(url)
+            # TODO: maybe update the other way around to let user override some values?
+            self._provider_metadata.update(metadata_response)
+            self._provider_needs_discovery = False
+
+        self._validate_metadata()
+
+        return self._provider_metadata
+
+    async def load_jwks(self, force: bool = False) -> JWKS:
+        """Load the JSON Web Key Set used to sign ID tokens.
+
+        If we're not using the ``userinfo_endpoint``, user infos are extracted
+        from the ID token, which is a JWT signed by keys given by the provider.
+        The keys are then cached.
+
+        Args:
+            force: Force reloading the keys.
+
+        Returns:
+            The key set
+
+            Looks like this::
+
+                {
+                    'keys': [
+                        {
+                            'kid': 'abcdef',
+                            'kty': 'RSA',
+                            'alg': 'RS256',
+                            'use': 'sig',
+                            'e': 'XXXX',
+                            'n': 'XXXX',
+                        }
+                    ]
+                }
+        """
+        if self._uses_userinfo:
+            # We're not using jwt signing, return an empty jwk set
+            return {"keys": []}
+
+        # First check if the JWKS are loaded in the provider metadata.
+        # It can happen either if the provider gives its JWKS in the discovery
+        # document directly or if it was already loaded once.
+        metadata = await self.load_metadata()
+        jwk_set = metadata.get("jwks")
+        if jwk_set is not None and not force:
+            return jwk_set
+
+        # Loading the JWKS using the `jwks_uri` metadata
+        uri = metadata.get("jwks_uri")
+        if not uri:
+            raise RuntimeError('Missing "jwks_uri" in metadata')
+
+        jwk_set = await self._http_client.get_json(uri)
+
+        # Caching the JWKS in the provider's metadata
+        self._provider_metadata["jwks"] = jwk_set
+        return jwk_set
+
+    async def _exchange_code(self, code: str) -> Token:
+        """Exchange an authorization code for a token.
+
+        This calls the ``token_endpoint`` with the authorization code we
+        received in the callback to exchange it for a token. The call uses the
+        ``ClientAuth`` to authenticate with the client with its ID and secret.
+
+        Args:
+            code: The autorization code we got from the callback.
+
+        Returns:
+            A dict containing various tokens.
+
+            May look like this::
+
+                {
+                    'token_type': 'bearer',
+                    'access_token': 'abcdef',
+                    'expires_in': 3599,
+                    'id_token': 'ghijkl',
+                    'refresh_token': 'mnopqr',
+                }
+
+        Raises:
+            OidcError: when the ``token_endpoint`` returned an error.
+        """
+        metadata = await self.load_metadata()
+        token_endpoint = metadata.get("token_endpoint")
+        headers = {
+            "Content-Type": "application/x-www-form-urlencoded",
+            "User-Agent": self._http_client.user_agent,
+            "Accept": "application/json",
+        }
+
+        args = {
+            "grant_type": "authorization_code",
+            "code": code,
+            "redirect_uri": self._callback_url,
+        }
+        body = urlencode(args, True)
+
+        # Fill the body/headers with credentials
+        uri, headers, body = self._client_auth.prepare(
+            method="POST", uri=token_endpoint, headers=headers, body=body
+        )
+        headers = {k: [v] for (k, v) in headers.items()}
+
+        # Do the actual request
+        # We're not using the SimpleHttpClient util methods as we don't want to
+        # check the HTTP status code and we do the body encoding ourself.
+        response = await self._http_client.request(
+            method="POST", uri=uri, data=body.encode("utf-8"), headers=headers,
+        )
+
+        # This is used in multiple error messages below
+        status = "{code} {phrase}".format(
+            code=response.code, phrase=response.phrase.decode("utf-8")
+        )
+
+        resp_body = await readBody(response)
+
+        if response.code >= 500:
+            # In case of a server error, we should first try to decode the body
+            # and check for an error field. If not, we respond with a generic
+            # error message.
+            try:
+                resp = json.loads(resp_body.decode("utf-8"))
+                error = resp["error"]
+                description = resp.get("error_description", error)
+            except (ValueError, KeyError):
+                # Catch ValueError for the JSON decoding and KeyError for the "error" field
+                error = "server_error"
+                description = (
+                    (
+                        'Authorization server responded with a "{status}" error '
+                        "while exchanging the authorization code."
+                    ).format(status=status),
+                )
+
+            raise OidcError(error, description)
+
+        # Since it is a not a 5xx code, body should be a valid JSON. It will
+        # raise if not.
+        resp = json.loads(resp_body.decode("utf-8"))
+
+        if "error" in resp:
+            error = resp["error"]
+            # In case the authorization server responded with an error field,
+            # it should be a 4xx code. If not, warn about it but don't do
+            # anything special and report the original error message.
+            if response.code < 400:
+                logger.debug(
+                    "Invalid response from the authorization server: "
+                    'responded with a "{status}" '
+                    "but body has an error field: {error!r}".format(
+                        status=status, error=resp["error"]
+                    )
+                )
+
+            description = resp.get("error_description", error)
+            raise OidcError(error, description)
+
+        # Now, this should not be an error. According to RFC6749 sec 5.1, it
+        # should be a 200 code. We're a bit more flexible than that, and will
+        # only throw on a 4xx code.
+        if response.code >= 400:
+            description = (
+                'Authorization server responded with a "{status}" error '
+                'but did not include an "error" field in its response.'.format(
+                    status=status
+                )
+            )
+            logger.warning(description)
+            # Body was still valid JSON. Might be useful to log it for debugging.
+            logger.warning("Code exchange response: {resp!r}".format(resp=resp))
+            raise OidcError("server_error", description)
+
+        return resp
+
+    async def _fetch_userinfo(self, token: Token) -> UserInfo:
+        """Fetch user informations from the ``userinfo_endpoint``.
+
+        Args:
+            token: the token given by the ``token_endpoint``.
+                Must include an ``access_token`` field.
+
+        Returns:
+            UserInfo: an object representing the user.
+        """
+        metadata = await self.load_metadata()
+
+        resp = await self._http_client.get_json(
+            metadata["userinfo_endpoint"],
+            headers={"Authorization": ["Bearer {}".format(token["access_token"])]},
+        )
+
+        return UserInfo(resp)
+
+    async def _parse_id_token(self, token: Token, nonce: str) -> UserInfo:
+        """Return an instance of UserInfo from token's ``id_token``.
+
+        Args:
+            token: the token given by the ``token_endpoint``.
+                Must include an ``id_token`` field.
+            nonce: the nonce value originally sent in the initial authorization
+                request. This value should match the one inside the token.
+
+        Returns:
+            An object representing the user.
+        """
+        metadata = await self.load_metadata()
+        claims_params = {
+            "nonce": nonce,
+            "client_id": self._client_auth.client_id,
+        }
+        if "access_token" in token:
+            # If we got an `access_token`, there should be an `at_hash` claim
+            # in the `id_token` that we can check against.
+            claims_params["access_token"] = token["access_token"]
+            claims_cls = CodeIDToken
+        else:
+            claims_cls = ImplicitIDToken
+
+        alg_values = metadata.get("id_token_signing_alg_values_supported", ["RS256"])
+
+        jwt = JsonWebToken(alg_values)
+
+        claim_options = {"iss": {"values": [metadata["issuer"]]}}
+
+        # Try to decode the keys in cache first, then retry by forcing the keys
+        # to be reloaded
+        jwk_set = await self.load_jwks()
+        try:
+            claims = jwt.decode(
+                token["id_token"],
+                key=jwk_set,
+                claims_cls=claims_cls,
+                claims_options=claim_options,
+                claims_params=claims_params,
+            )
+        except ValueError:
+            jwk_set = await self.load_jwks(force=True)  # try reloading the jwks
+            claims = jwt.decode(
+                token["id_token"],
+                key=jwk_set,
+                claims_cls=claims_cls,
+                claims_options=claim_options,
+                claims_params=claims_params,
+            )
+
+        claims.validate(leeway=120)  # allows 2 min of clock skew
+        return UserInfo(claims)
+
+    async def handle_redirect_request(
+        self, request: SynapseRequest, client_redirect_url: bytes
+    ) -> None:
+        """Handle an incoming request to /login/sso/redirect
+
+        It redirects the browser to the authorization endpoint with a few
+        parameters:
+
+          - ``client_id``: the client ID set in ``oidc_config.client_id``
+          - ``response_type``: ``code``
+          - ``redirect_uri``: the callback URL ; ``{base url}/_synapse/oidc/callback``
+          - ``scope``: the list of scopes set in ``oidc_config.scopes``
+          - ``state``: a random string
+          - ``nonce``: a random string
+
+        In addition to redirecting the client, we are setting a cookie with
+        a signed macaroon token containing the state, the nonce and the
+        client_redirect_url params. Those are then checked when the client
+        comes back from the provider.
+
+
+        Args:
+            request: the incoming request from the browser.
+                We'll respond to it with a redirect and a cookie.
+            client_redirect_url: the URL that we should redirect the client to
+                when everything is done
+        """
+
+        state = generate_token()
+        nonce = generate_token()
+
+        cookie = self._generate_oidc_session_token(
+            state=state, nonce=nonce, client_redirect_url=client_redirect_url.decode(),
+        )
+        request.addCookie(
+            SESSION_COOKIE_NAME,
+            cookie,
+            path="/_synapse/oidc",
+            max_age="3600",
+            httpOnly=True,
+            sameSite="lax",
+        )
+
+        metadata = await self.load_metadata()
+        authorization_endpoint = metadata.get("authorization_endpoint")
+        uri = prepare_grant_uri(
+            authorization_endpoint,
+            client_id=self._client_auth.client_id,
+            response_type="code",
+            redirect_uri=self._callback_url,
+            scope=self._scopes,
+            state=state,
+            nonce=nonce,
+        )
+        request.redirect(uri)
+        finish_request(request)
+
+    async def handle_oidc_callback(self, request: SynapseRequest) -> None:
+        """Handle an incoming request to /_synapse/oidc/callback
+
+        Since we might want to display OIDC-related errors in a user-friendly
+        way, we don't raise SynapseError from here. Instead, we call
+        ``self._render_error`` which displays an HTML page for the error.
+
+        Most of the OpenID Connect logic happens here:
+
+          - first, we check if there was any error returned by the provider and
+            display it
+          - then we fetch the session cookie, decode and verify it
+          - the ``state`` query parameter should match with the one stored in the
+            session cookie
+          - once we known this session is legit, exchange the code with the
+            provider using the ``token_endpoint`` (see ``_exchange_code``)
+          - once we have the token, use it to either extract the UserInfo from
+            the ``id_token`` (``_parse_id_token``), or use the ``access_token``
+            to fetch UserInfo from the ``userinfo_endpoint``
+            (``_fetch_userinfo``)
+          - map those UserInfo to a Matrix user (``_map_userinfo_to_user``) and
+            finish the login
+
+        Args:
+            request: the incoming request from the browser.
+        """
+
+        # The provider might redirect with an error.
+        # In that case, just display it as-is.
+        if b"error" in request.args:
+            error = request.args[b"error"][0].decode()
+            description = request.args.get(b"error_description", [b""])[0].decode()
+
+            # Most of the errors returned by the provider could be due by
+            # either the provider misbehaving or Synapse being misconfigured.
+            # The only exception of that is "access_denied", where the user
+            # probably cancelled the login flow. In other cases, log those errors.
+            if error != "access_denied":
+                logger.error("Error from the OIDC provider: %s %s", error, description)
+
+            self._render_error(request, error, description)
+            return
+
+        # Fetch the session cookie
+        session = request.getCookie(SESSION_COOKIE_NAME)
+        if session is None:
+            logger.info("No session cookie found")
+            self._render_error(request, "missing_session", "No session cookie found")
+            return
+
+        # Remove the cookie. There is a good chance that if the callback failed
+        # once, it will fail next time and the code will already be exchanged.
+        # Removing it early avoids spamming the provider with token requests.
+        request.addCookie(
+            SESSION_COOKIE_NAME,
+            b"",
+            path="/_synapse/oidc",
+            expires="Thu, Jan 01 1970 00:00:00 UTC",
+            httpOnly=True,
+            sameSite="lax",
+        )
+
+        # Check for the state query parameter
+        if b"state" not in request.args:
+            logger.info("State parameter is missing")
+            self._render_error(request, "invalid_request", "State parameter is missing")
+            return
+
+        state = request.args[b"state"][0].decode()
+
+        # Deserialize the session token and verify it.
+        try:
+            nonce, client_redirect_url = self._verify_oidc_session_token(session, state)
+        except MacaroonDeserializationException as e:
+            logger.exception("Invalid session")
+            self._render_error(request, "invalid_session", str(e))
+            return
+        except MacaroonInvalidSignatureException as e:
+            logger.exception("Could not verify session")
+            self._render_error(request, "mismatching_session", str(e))
+            return
+
+        # Exchange the code with the provider
+        if b"code" not in request.args:
+            logger.info("Code parameter is missing")
+            self._render_error(request, "invalid_request", "Code parameter is missing")
+            return
+
+        logger.info("Exchanging code")
+        code = request.args[b"code"][0].decode()
+        try:
+            token = await self._exchange_code(code)
+        except OidcError as e:
+            logger.exception("Could not exchange code")
+            self._render_error(request, e.error, e.error_description)
+            return
+
+        # Now that we have a token, get the userinfo, either by decoding the
+        # `id_token` or by fetching the `userinfo_endpoint`.
+        if self._uses_userinfo:
+            logger.info("Fetching userinfo")
+            try:
+                userinfo = await self._fetch_userinfo(token)
+            except Exception as e:
+                logger.exception("Could not fetch userinfo")
+                self._render_error(request, "fetch_error", str(e))
+                return
+        else:
+            logger.info("Extracting userinfo from id_token")
+            try:
+                userinfo = await self._parse_id_token(token, nonce=nonce)
+            except Exception as e:
+                logger.exception("Invalid id_token")
+                self._render_error(request, "invalid_token", str(e))
+                return
+
+        # Call the mapper to register/login the user
+        try:
+            user_id = await self._map_userinfo_to_user(userinfo, token)
+        except MappingException as e:
+            logger.exception("Could not map user")
+            self._render_error(request, "mapping_error", str(e))
+            return
+
+        # and finally complete the login
+        await self._auth_handler.complete_sso_login(
+            user_id, request, client_redirect_url
+        )
+
+    def _generate_oidc_session_token(
+        self,
+        state: str,
+        nonce: str,
+        client_redirect_url: str,
+        duration_in_ms: int = (60 * 60 * 1000),
+    ) -> str:
+        """Generates a signed token storing data about an OIDC session.
+
+        When Synapse initiates an authorization flow, it creates a random state
+        and a random nonce. Those parameters are given to the provider and
+        should be verified when the client comes back from the provider.
+        It is also used to store the client_redirect_url, which is used to
+        complete the SSO login flow.
+
+        Args:
+            state: The ``state`` parameter passed to the OIDC provider.
+            nonce: The ``nonce`` parameter passed to the OIDC provider.
+            client_redirect_url: The URL the client gave when it initiated the
+                flow.
+            duration_in_ms: An optional duration for the token in milliseconds.
+                Defaults to an hour.
+
+        Returns:
+            A signed macaroon token with the session informations.
+        """
+        macaroon = pymacaroons.Macaroon(
+            location=self._server_name, identifier="key", key=self._macaroon_secret_key,
+        )
+        macaroon.add_first_party_caveat("gen = 1")
+        macaroon.add_first_party_caveat("type = session")
+        macaroon.add_first_party_caveat("state = %s" % (state,))
+        macaroon.add_first_party_caveat("nonce = %s" % (nonce,))
+        macaroon.add_first_party_caveat(
+            "client_redirect_url = %s" % (client_redirect_url,)
+        )
+        now = self._clock.time_msec()
+        expiry = now + duration_in_ms
+        macaroon.add_first_party_caveat("time < %d" % (expiry,))
+        return macaroon.serialize()
+
+    def _verify_oidc_session_token(self, session: str, state: str) -> Tuple[str, str]:
+        """Verifies and extract an OIDC session token.
+
+        This verifies that a given session token was issued by this homeserver
+        and extract the nonce and client_redirect_url caveats.
+
+        Args:
+            session: The session token to verify
+            state: The state the OIDC provider gave back
+
+        Returns:
+            The nonce and the client_redirect_url for this session
+        """
+        macaroon = pymacaroons.Macaroon.deserialize(session)
+
+        v = pymacaroons.Verifier()
+        v.satisfy_exact("gen = 1")
+        v.satisfy_exact("type = session")
+        v.satisfy_exact("state = %s" % (state,))
+        v.satisfy_general(lambda c: c.startswith("nonce = "))
+        v.satisfy_general(lambda c: c.startswith("client_redirect_url = "))
+        v.satisfy_general(self._verify_expiry)
+
+        v.verify(macaroon, self._macaroon_secret_key)
+
+        # Extract the `nonce` and `client_redirect_url` from the token
+        nonce = self._get_value_from_macaroon(macaroon, "nonce")
+        client_redirect_url = self._get_value_from_macaroon(
+            macaroon, "client_redirect_url"
+        )
+
+        return nonce, client_redirect_url
+
+    def _get_value_from_macaroon(self, macaroon: pymacaroons.Macaroon, key: str) -> str:
+        """Extracts a caveat value from a macaroon token.
+
+        Args:
+            macaroon: the token
+            key: the key of the caveat to extract
+
+        Returns:
+            The extracted value
+
+        Raises:
+            Exception: if the caveat was not in the macaroon
+        """
+        prefix = key + " = "
+        for caveat in macaroon.caveats:
+            if caveat.caveat_id.startswith(prefix):
+                return caveat.caveat_id[len(prefix) :]
+        raise Exception("No %s caveat in macaroon" % (key,))
+
+    def _verify_expiry(self, caveat: str) -> bool:
+        prefix = "time < "
+        if not caveat.startswith(prefix):
+            return False
+        expiry = int(caveat[len(prefix) :])
+        now = self._clock.time_msec()
+        return now < expiry
+
+    async def _map_userinfo_to_user(self, userinfo: UserInfo, token: Token) -> str:
+        """Maps a UserInfo object to a mxid.
+
+        UserInfo should have a claim that uniquely identifies users. This claim
+        is usually `sub`, but can be configured with `oidc_config.subject_claim`.
+        It is then used as an `external_id`.
+
+        If we don't find the user that way, we should register the user,
+        mapping the localpart and the display name from the UserInfo.
+
+        If a user already exists with the mxid we've mapped, raise an exception.
+
+        Args:
+            userinfo: an object representing the user
+            token: a dict with the tokens obtained from the provider
+
+        Raises:
+            MappingException: if there was an error while mapping some properties
+
+        Returns:
+            The mxid of the user
+        """
+        try:
+            remote_user_id = self._user_mapping_provider.get_remote_user_id(userinfo)
+        except Exception as e:
+            raise MappingException(
+                "Failed to extract subject from OIDC response: %s" % (e,)
+            )
+
+        logger.info(
+            "Looking for existing mapping for user %s:%s",
+            self._auth_provider_id,
+            remote_user_id,
+        )
+
+        registered_user_id = await self._datastore.get_user_by_external_id(
+            self._auth_provider_id, remote_user_id,
+        )
+
+        if registered_user_id is not None:
+            logger.info("Found existing mapping %s", registered_user_id)
+            return registered_user_id
+
+        try:
+            attributes = await self._user_mapping_provider.map_user_attributes(
+                userinfo, token
+            )
+        except Exception as e:
+            raise MappingException(
+                "Could not extract user attributes from OIDC response: " + str(e)
+            )
+
+        logger.debug(
+            "Retrieved user attributes from user mapping provider: %r", attributes
+        )
+
+        if not attributes["localpart"]:
+            raise MappingException("localpart is empty")
+
+        localpart = map_username_to_mxid_localpart(attributes["localpart"])
+
+        user_id = UserID(localpart, self._hostname)
+        if await self._datastore.get_users_by_id_case_insensitive(user_id.to_string()):
+            # This mxid is taken
+            raise MappingException(
+                "mxid '{}' is already taken".format(user_id.to_string())
+            )
+
+        # It's the first time this user is logging in and the mapped mxid was
+        # not taken, register the user
+        registered_user_id = await self._registration_handler.register_user(
+            localpart=localpart, default_display_name=attributes["display_name"],
+        )
+
+        await self._datastore.record_user_external_id(
+            self._auth_provider_id, remote_user_id, registered_user_id,
+        )
+        return registered_user_id
+
+
+UserAttribute = TypedDict(
+    "UserAttribute", {"localpart": str, "display_name": Optional[str]}
+)
+C = TypeVar("C")
+
+
+class OidcMappingProvider(Generic[C]):
+    """A mapping provider maps a UserInfo object to user attributes.
+
+    It should provide the API described by this class.
+    """
+
+    def __init__(self, config: C):
+        """
+        Args:
+            config: A custom config object from this module, parsed by ``parse_config()``
+        """
+
+    @staticmethod
+    def parse_config(config: dict) -> C:
+        """Parse the dict provided by the homeserver's config
+
+        Args:
+            config: A dictionary containing configuration options for this provider
+
+        Returns:
+            A custom config object for this module
+        """
+        raise NotImplementedError()
+
+    def get_remote_user_id(self, userinfo: UserInfo) -> str:
+        """Get a unique user ID for this user.
+
+        Usually, in an OIDC-compliant scenario, it should be the ``sub`` claim from the UserInfo object.
+
+        Args:
+            userinfo: An object representing the user given by the OIDC provider
+
+        Returns:
+            A unique user ID
+        """
+        raise NotImplementedError()
+
+    async def map_user_attributes(
+        self, userinfo: UserInfo, token: Token
+    ) -> UserAttribute:
+        """Map a ``UserInfo`` objects into user attributes.
+
+        Args:
+            userinfo: An object representing the user given by the OIDC provider
+            token: A dict with the tokens returned by the provider
+
+        Returns:
+            A dict containing the ``localpart`` and (optionally) the ``display_name``
+        """
+        raise NotImplementedError()
+
+
+# Used to clear out "None" values in templates
+def jinja_finalize(thing):
+    return thing if thing is not None else ""
+
+
+env = Environment(finalize=jinja_finalize)
+
+
+@attr.s
+class JinjaOidcMappingConfig:
+    subject_claim = attr.ib()  # type: str
+    localpart_template = attr.ib()  # type: Template
+    display_name_template = attr.ib()  # type: Optional[Template]
+
+
+class JinjaOidcMappingProvider(OidcMappingProvider[JinjaOidcMappingConfig]):
+    """An implementation of a mapping provider based on Jinja templates.
+
+    This is the default mapping provider.
+    """
+
+    def __init__(self, config: JinjaOidcMappingConfig):
+        self._config = config
+
+    @staticmethod
+    def parse_config(config: dict) -> JinjaOidcMappingConfig:
+        subject_claim = config.get("subject_claim", "sub")
+
+        if "localpart_template" not in config:
+            raise ConfigError(
+                "missing key: oidc_config.user_mapping_provider.config.localpart_template"
+            )
+
+        try:
+            localpart_template = env.from_string(config["localpart_template"])
+        except Exception as e:
+            raise ConfigError(
+                "invalid jinja template for oidc_config.user_mapping_provider.config.localpart_template: %r"
+                % (e,)
+            )
+
+        display_name_template = None  # type: Optional[Template]
+        if "display_name_template" in config:
+            try:
+                display_name_template = env.from_string(config["display_name_template"])
+            except Exception as e:
+                raise ConfigError(
+                    "invalid jinja template for oidc_config.user_mapping_provider.config.display_name_template: %r"
+                    % (e,)
+                )
+
+        return JinjaOidcMappingConfig(
+            subject_claim=subject_claim,
+            localpart_template=localpart_template,
+            display_name_template=display_name_template,
+        )
+
+    def get_remote_user_id(self, userinfo: UserInfo) -> str:
+        return userinfo[self._config.subject_claim]
+
+    async def map_user_attributes(
+        self, userinfo: UserInfo, token: Token
+    ) -> UserAttribute:
+        localpart = self._config.localpart_template.render(user=userinfo).strip()
+
+        display_name = None  # type: Optional[str]
+        if self._config.display_name_template is not None:
+            display_name = self._config.display_name_template.render(
+                user=userinfo
+            ).strip()
+
+            if display_name == "":
+                display_name = None
+
+        return UserAttribute(localpart=localpart, display_name=display_name)
diff --git a/synapse/http/client.py b/synapse/http/client.py
index 3797545824..58eb47c69c 100644
--- a/synapse/http/client.py
+++ b/synapse/http/client.py
@@ -359,6 +359,7 @@ class SimpleHttpClient(object):
         actual_headers = {
             b"Content-Type": [b"application/x-www-form-urlencoded"],
             b"User-Agent": [self.user_agent],
+            b"Accept": [b"application/json"],
         }
         if headers:
             actual_headers.update(headers)
@@ -399,6 +400,7 @@ class SimpleHttpClient(object):
         actual_headers = {
             b"Content-Type": [b"application/json"],
             b"User-Agent": [self.user_agent],
+            b"Accept": [b"application/json"],
         }
         if headers:
             actual_headers.update(headers)
@@ -434,6 +436,10 @@ class SimpleHttpClient(object):
 
             ValueError: if the response was not JSON
         """
+        actual_headers = {b"Accept": [b"application/json"]}
+        if headers:
+            actual_headers.update(headers)
+
         body = yield self.get_raw(uri, args, headers=headers)
         return json.loads(body)
 
@@ -467,6 +473,7 @@ class SimpleHttpClient(object):
         actual_headers = {
             b"Content-Type": [b"application/json"],
             b"User-Agent": [self.user_agent],
+            b"Accept": [b"application/json"],
         }
         if headers:
             actual_headers.update(headers)
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 39c99a2802..8b4312e5a3 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -92,6 +92,7 @@ CONDITIONAL_REQUIREMENTS = {
         'eliot<1.8.0;python_version<"3.5.3"',
     ],
     "saml2": ["pysaml2>=4.5.0"],
+    "oidc": ["authlib>=0.14.0"],
     "systemd": ["systemd-python>=231"],
     "url_preview": ["lxml>=3.5.0"],
     "test": ["mock>=2.0", "parameterized"],
diff --git a/synapse/res/templates/sso_error.html b/synapse/res/templates/sso_error.html
new file mode 100644
index 0000000000..43a211386b
--- /dev/null
+++ b/synapse/res/templates/sso_error.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <title>SSO error</title>
+</head>
+<body>
+    <p>Oops! Something went wrong during authentication.</p>
+    <p>
+        Try logging in again from your Matrix client and if the problem persists
+        please contact the server's administrator.
+    </p>
+    <p>Error: <code>{{ error }}</code></p>
+    {% if error_description %}
+    <pre><code>{{ error_description }}</code></pre>
+    {% endif %}
+</body>
+</html>
diff --git a/synapse/rest/client/v1/login.py b/synapse/rest/client/v1/login.py
index 4de2f97d06..de7eca21f8 100644
--- a/synapse/rest/client/v1/login.py
+++ b/synapse/rest/client/v1/login.py
@@ -83,6 +83,7 @@ class LoginRestServlet(RestServlet):
         self.jwt_algorithm = hs.config.jwt_algorithm
         self.saml2_enabled = hs.config.saml2_enabled
         self.cas_enabled = hs.config.cas_enabled
+        self.oidc_enabled = hs.config.oidc_enabled
         self.auth_handler = self.hs.get_auth_handler()
         self.registration_handler = hs.get_registration_handler()
         self.handlers = hs.get_handlers()
@@ -96,9 +97,7 @@ class LoginRestServlet(RestServlet):
         flows = []
         if self.jwt_enabled:
             flows.append({"type": LoginRestServlet.JWT_TYPE})
-        if self.saml2_enabled:
-            flows.append({"type": LoginRestServlet.SSO_TYPE})
-            flows.append({"type": LoginRestServlet.TOKEN_TYPE})
+
         if self.cas_enabled:
             flows.append({"type": LoginRestServlet.SSO_TYPE})
 
@@ -114,6 +113,11 @@ class LoginRestServlet(RestServlet):
             # fall back to the fallback API if they don't understand one of the
             # login flow types returned.
             flows.append({"type": LoginRestServlet.TOKEN_TYPE})
+        elif self.saml2_enabled:
+            flows.append({"type": LoginRestServlet.SSO_TYPE})
+            flows.append({"type": LoginRestServlet.TOKEN_TYPE})
+        elif self.oidc_enabled:
+            flows.append({"type": LoginRestServlet.SSO_TYPE})
 
         flows.extend(
             ({"type": t} for t in self.auth_handler.get_supported_login_types())
@@ -465,6 +469,22 @@ class SAMLRedirectServlet(BaseSSORedirectServlet):
         return self._saml_handler.handle_redirect_request(client_redirect_url)
 
 
+class OIDCRedirectServlet(RestServlet):
+    """Implementation for /login/sso/redirect for the OIDC login flow."""
+
+    PATTERNS = client_patterns("/login/sso/redirect", v1=True)
+
+    def __init__(self, hs):
+        self._oidc_handler = hs.get_oidc_handler()
+
+    async def on_GET(self, request):
+        args = request.args
+        if b"redirectUrl" not in args:
+            return 400, "Redirect URL not specified for SSO auth"
+        client_redirect_url = args[b"redirectUrl"][0]
+        await self._oidc_handler.handle_redirect_request(request, client_redirect_url)
+
+
 def register_servlets(hs, http_server):
     LoginRestServlet(hs).register(http_server)
     if hs.config.cas_enabled:
@@ -472,3 +492,5 @@ def register_servlets(hs, http_server):
         CasTicketServlet(hs).register(http_server)
     elif hs.config.saml2_enabled:
         SAMLRedirectServlet(hs).register(http_server)
+    elif hs.config.oidc_enabled:
+        OIDCRedirectServlet(hs).register(http_server)
diff --git a/synapse/rest/oidc/__init__.py b/synapse/rest/oidc/__init__.py
new file mode 100644
index 0000000000..d958dd65bb
--- /dev/null
+++ b/synapse/rest/oidc/__init__.py
@@ -0,0 +1,27 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Quentin Gliech
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import logging
+
+from twisted.web.resource import Resource
+
+from synapse.rest.oidc.callback_resource import OIDCCallbackResource
+
+logger = logging.getLogger(__name__)
+
+
+class OIDCResource(Resource):
+    def __init__(self, hs):
+        Resource.__init__(self)
+        self.putChild(b"callback", OIDCCallbackResource(hs))
diff --git a/synapse/rest/oidc/callback_resource.py b/synapse/rest/oidc/callback_resource.py
new file mode 100644
index 0000000000..c03194f001
--- /dev/null
+++ b/synapse/rest/oidc/callback_resource.py
@@ -0,0 +1,31 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Quentin Gliech
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import logging
+
+from synapse.http.server import DirectServeResource, wrap_html_request_handler
+
+logger = logging.getLogger(__name__)
+
+
+class OIDCCallbackResource(DirectServeResource):
+    isLeaf = 1
+
+    def __init__(self, hs):
+        super().__init__()
+        self._oidc_handler = hs.get_oidc_handler()
+
+    @wrap_html_request_handler
+    async def _async_render_GET(self, request):
+        return await self._oidc_handler.handle_oidc_callback(request)
diff --git a/synapse/server.py b/synapse/server.py
index bf97a16c09..b4aea81e24 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -204,6 +204,7 @@ class HomeServer(object):
         "account_validity_handler",
         "cas_handler",
         "saml_handler",
+        "oidc_handler",
         "event_client_serializer",
         "password_policy_handler",
         "storage",
@@ -562,6 +563,11 @@ class HomeServer(object):
 
         return SamlHandler(self)
 
+    def build_oidc_handler(self):
+        from synapse.handlers.oidc_handler import OidcHandler
+
+        return OidcHandler(self)
+
     def build_event_client_serializer(self):
         return EventClientSerializer(self)
 
diff --git a/synapse/server.pyi b/synapse/server.pyi
index 18043a2593..31a9cc0389 100644
--- a/synapse/server.pyi
+++ b/synapse/server.pyi
@@ -13,6 +13,7 @@ import synapse.handlers.device
 import synapse.handlers.e2e_keys
 import synapse.handlers.message
 import synapse.handlers.presence
+import synapse.handlers.register
 import synapse.handlers.room
 import synapse.handlers.room_member
 import synapse.handlers.set_password
@@ -128,3 +129,7 @@ class HomeServer(object):
         pass
     def get_storage(self) -> synapse.storage.Storage:
         pass
+    def get_registration_handler(self) -> synapse.handlers.register.RegistrationHandler:
+        pass
+    def get_macaroon_generator(self) -> synapse.handlers.auth.MacaroonGenerator:
+        pass
diff --git a/tests/handlers/test_oidc.py b/tests/handlers/test_oidc.py
new file mode 100644
index 0000000000..61963aa90d
--- /dev/null
+++ b/tests/handlers/test_oidc.py
@@ -0,0 +1,565 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Quentin Gliech
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import json
+from urllib.parse import parse_qs, urlparse
+
+from mock import Mock, patch
+
+import attr
+import pymacaroons
+
+from twisted.internet import defer
+from twisted.python.failure import Failure
+from twisted.web._newclient import ResponseDone
+
+from synapse.handlers.oidc_handler import (
+    MappingException,
+    OidcError,
+    OidcHandler,
+    OidcMappingProvider,
+)
+from synapse.types import UserID
+
+from tests.unittest import HomeserverTestCase, override_config
+
+
+@attr.s
+class FakeResponse:
+    code = attr.ib()
+    body = attr.ib()
+    phrase = attr.ib()
+
+    def deliverBody(self, protocol):
+        protocol.dataReceived(self.body)
+        protocol.connectionLost(Failure(ResponseDone()))
+
+
+# These are a few constants that are used as config parameters in the tests.
+ISSUER = "https://issuer/"
+CLIENT_ID = "test-client-id"
+CLIENT_SECRET = "test-client-secret"
+BASE_URL = "https://synapse/"
+CALLBACK_URL = BASE_URL + "_synapse/oidc/callback"
+SCOPES = ["openid"]
+
+AUTHORIZATION_ENDPOINT = ISSUER + "authorize"
+TOKEN_ENDPOINT = ISSUER + "token"
+USERINFO_ENDPOINT = ISSUER + "userinfo"
+WELL_KNOWN = ISSUER + ".well-known/openid-configuration"
+JWKS_URI = ISSUER + ".well-known/jwks.json"
+
+# config for common cases
+COMMON_CONFIG = {
+    "discover": False,
+    "authorization_endpoint": AUTHORIZATION_ENDPOINT,
+    "token_endpoint": TOKEN_ENDPOINT,
+    "jwks_uri": JWKS_URI,
+}
+
+
+# The cookie name and path don't really matter, just that it has to be coherent
+# between the callback & redirect handlers.
+COOKIE_NAME = b"oidc_session"
+COOKIE_PATH = "/_synapse/oidc"
+
+MockedMappingProvider = Mock(OidcMappingProvider)
+
+
+def simple_async_mock(return_value=None, raises=None):
+    # AsyncMock is not available in python3.5, this mimics part of its behaviour
+    async def cb(*args, **kwargs):
+        if raises:
+            raise raises
+        return return_value
+
+    return Mock(side_effect=cb)
+
+
+async def get_json(url):
+    # Mock get_json calls to handle jwks & oidc discovery endpoints
+    if url == WELL_KNOWN:
+        # Minimal discovery document, as defined in OpenID.Discovery
+        # https://openid.net/specs/openid-connect-discovery-1_0.html#ProviderMetadata
+        return {
+            "issuer": ISSUER,
+            "authorization_endpoint": AUTHORIZATION_ENDPOINT,
+            "token_endpoint": TOKEN_ENDPOINT,
+            "jwks_uri": JWKS_URI,
+            "userinfo_endpoint": USERINFO_ENDPOINT,
+            "response_types_supported": ["code"],
+            "subject_types_supported": ["public"],
+            "id_token_signing_alg_values_supported": ["RS256"],
+        }
+    elif url == JWKS_URI:
+        return {"keys": []}
+
+
+class OidcHandlerTestCase(HomeserverTestCase):
+    def make_homeserver(self, reactor, clock):
+
+        self.http_client = Mock(spec=["get_json"])
+        self.http_client.get_json.side_effect = get_json
+        self.http_client.user_agent = "Synapse Test"
+
+        config = self.default_config()
+        config["public_baseurl"] = BASE_URL
+        oidc_config = config.get("oidc_config", {})
+        oidc_config["enabled"] = True
+        oidc_config["client_id"] = CLIENT_ID
+        oidc_config["client_secret"] = CLIENT_SECRET
+        oidc_config["issuer"] = ISSUER
+        oidc_config["scopes"] = SCOPES
+        oidc_config["user_mapping_provider"] = {
+            "module": __name__ + ".MockedMappingProvider"
+        }
+        config["oidc_config"] = oidc_config
+
+        hs = self.setup_test_homeserver(
+            http_client=self.http_client,
+            proxied_http_client=self.http_client,
+            config=config,
+        )
+
+        self.handler = OidcHandler(hs)
+
+        return hs
+
+    def metadata_edit(self, values):
+        return patch.dict(self.handler._provider_metadata, values)
+
+    def assertRenderedError(self, error, error_description=None):
+        args = self.handler._render_error.call_args[0]
+        self.assertEqual(args[1], error)
+        if error_description is not None:
+            self.assertEqual(args[2], error_description)
+        # Reset the render_error mock
+        self.handler._render_error.reset_mock()
+
+    def test_config(self):
+        """Basic config correctly sets up the callback URL and client auth correctly."""
+        self.assertEqual(self.handler._callback_url, CALLBACK_URL)
+        self.assertEqual(self.handler._client_auth.client_id, CLIENT_ID)
+        self.assertEqual(self.handler._client_auth.client_secret, CLIENT_SECRET)
+
+    @override_config({"oidc_config": {"discover": True}})
+    @defer.inlineCallbacks
+    def test_discovery(self):
+        """The handler should discover the endpoints from OIDC discovery document."""
+        # This would throw if some metadata were invalid
+        metadata = yield defer.ensureDeferred(self.handler.load_metadata())
+        self.http_client.get_json.assert_called_once_with(WELL_KNOWN)
+
+        self.assertEqual(metadata.issuer, ISSUER)
+        self.assertEqual(metadata.authorization_endpoint, AUTHORIZATION_ENDPOINT)
+        self.assertEqual(metadata.token_endpoint, TOKEN_ENDPOINT)
+        self.assertEqual(metadata.jwks_uri, JWKS_URI)
+        # FIXME: it seems like authlib does not have that defined in its metadata models
+        # self.assertEqual(metadata.userinfo_endpoint, USERINFO_ENDPOINT)
+
+        # subsequent calls should be cached
+        self.http_client.reset_mock()
+        yield defer.ensureDeferred(self.handler.load_metadata())
+        self.http_client.get_json.assert_not_called()
+
+    @override_config({"oidc_config": COMMON_CONFIG})
+    @defer.inlineCallbacks
+    def test_no_discovery(self):
+        """When discovery is disabled, it should not try to load from discovery document."""
+        yield defer.ensureDeferred(self.handler.load_metadata())
+        self.http_client.get_json.assert_not_called()
+
+    @override_config({"oidc_config": COMMON_CONFIG})
+    @defer.inlineCallbacks
+    def test_load_jwks(self):
+        """JWKS loading is done once (then cached) if used."""
+        jwks = yield defer.ensureDeferred(self.handler.load_jwks())
+        self.http_client.get_json.assert_called_once_with(JWKS_URI)
+        self.assertEqual(jwks, {"keys": []})
+
+        # subsequent calls should be cached…
+        self.http_client.reset_mock()
+        yield defer.ensureDeferred(self.handler.load_jwks())
+        self.http_client.get_json.assert_not_called()
+
+        # …unless forced
+        self.http_client.reset_mock()
+        yield defer.ensureDeferred(self.handler.load_jwks(force=True))
+        self.http_client.get_json.assert_called_once_with(JWKS_URI)
+
+        # Throw if the JWKS uri is missing
+        with self.metadata_edit({"jwks_uri": None}):
+            with self.assertRaises(RuntimeError):
+                yield defer.ensureDeferred(self.handler.load_jwks(force=True))
+
+        # Return empty key set if JWKS are not used
+        self.handler._scopes = []  # not asking the openid scope
+        self.http_client.get_json.reset_mock()
+        jwks = yield defer.ensureDeferred(self.handler.load_jwks(force=True))
+        self.http_client.get_json.assert_not_called()
+        self.assertEqual(jwks, {"keys": []})
+
+    @override_config({"oidc_config": COMMON_CONFIG})
+    def test_validate_config(self):
+        """Provider metadatas are extensively validated."""
+        h = self.handler
+
+        # Default test config does not throw
+        h._validate_metadata()
+
+        with self.metadata_edit({"issuer": None}):
+            self.assertRaisesRegex(ValueError, "issuer", h._validate_metadata)
+
+        with self.metadata_edit({"issuer": "http://insecure/"}):
+            self.assertRaisesRegex(ValueError, "issuer", h._validate_metadata)
+
+        with self.metadata_edit({"issuer": "https://invalid/?because=query"}):
+            self.assertRaisesRegex(ValueError, "issuer", h._validate_metadata)
+
+        with self.metadata_edit({"authorization_endpoint": None}):
+            self.assertRaisesRegex(
+                ValueError, "authorization_endpoint", h._validate_metadata
+            )
+
+        with self.metadata_edit({"authorization_endpoint": "http://insecure/auth"}):
+            self.assertRaisesRegex(
+                ValueError, "authorization_endpoint", h._validate_metadata
+            )
+
+        with self.metadata_edit({"token_endpoint": None}):
+            self.assertRaisesRegex(ValueError, "token_endpoint", h._validate_metadata)
+
+        with self.metadata_edit({"token_endpoint": "http://insecure/token"}):
+            self.assertRaisesRegex(ValueError, "token_endpoint", h._validate_metadata)
+
+        with self.metadata_edit({"jwks_uri": None}):
+            self.assertRaisesRegex(ValueError, "jwks_uri", h._validate_metadata)
+
+        with self.metadata_edit({"jwks_uri": "http://insecure/jwks.json"}):
+            self.assertRaisesRegex(ValueError, "jwks_uri", h._validate_metadata)
+
+        with self.metadata_edit({"response_types_supported": ["id_token"]}):
+            self.assertRaisesRegex(
+                ValueError, "response_types_supported", h._validate_metadata
+            )
+
+        with self.metadata_edit(
+            {"token_endpoint_auth_methods_supported": ["client_secret_basic"]}
+        ):
+            # should not throw, as client_secret_basic is the default auth method
+            h._validate_metadata()
+
+        with self.metadata_edit(
+            {"token_endpoint_auth_methods_supported": ["client_secret_post"]}
+        ):
+            self.assertRaisesRegex(
+                ValueError,
+                "token_endpoint_auth_methods_supported",
+                h._validate_metadata,
+            )
+
+        # Tests for configs that the userinfo endpoint
+        self.assertFalse(h._uses_userinfo)
+        h._scopes = []  # do not request the openid scope
+        self.assertTrue(h._uses_userinfo)
+        self.assertRaisesRegex(ValueError, "userinfo_endpoint", h._validate_metadata)
+
+        with self.metadata_edit(
+            {"userinfo_endpoint": USERINFO_ENDPOINT, "jwks_uri": None}
+        ):
+            # Shouldn't raise with a valid userinfo, even without
+            h._validate_metadata()
+
+    @override_config({"oidc_config": {"skip_verification": True}})
+    def test_skip_verification(self):
+        """Provider metadata validation can be disabled by config."""
+        with self.metadata_edit({"issuer": "http://insecure"}):
+            # This should not throw
+            self.handler._validate_metadata()
+
+    @defer.inlineCallbacks
+    def test_redirect_request(self):
+        """The redirect request has the right arguments & generates a valid session cookie."""
+        req = Mock(spec=["addCookie", "redirect", "finish"])
+        yield defer.ensureDeferred(
+            self.handler.handle_redirect_request(req, b"http://client/redirect")
+        )
+        url = req.redirect.call_args[0][0]
+        url = urlparse(url)
+        auth_endpoint = urlparse(AUTHORIZATION_ENDPOINT)
+
+        self.assertEqual(url.scheme, auth_endpoint.scheme)
+        self.assertEqual(url.netloc, auth_endpoint.netloc)
+        self.assertEqual(url.path, auth_endpoint.path)
+
+        params = parse_qs(url.query)
+        self.assertEqual(params["redirect_uri"], [CALLBACK_URL])
+        self.assertEqual(params["response_type"], ["code"])
+        self.assertEqual(params["scope"], [" ".join(SCOPES)])
+        self.assertEqual(params["client_id"], [CLIENT_ID])
+        self.assertEqual(len(params["state"]), 1)
+        self.assertEqual(len(params["nonce"]), 1)
+
+        # Check what is in the cookie
+        # note: python3.5 mock does not have the .called_once() method
+        calls = req.addCookie.call_args_list
+        self.assertEqual(len(calls), 1)  # called once
+        # For some reason, call.args does not work with python3.5
+        args = calls[0][0]
+        kwargs = calls[0][1]
+        self.assertEqual(args[0], COOKIE_NAME)
+        self.assertEqual(kwargs["path"], COOKIE_PATH)
+        cookie = args[1]
+
+        macaroon = pymacaroons.Macaroon.deserialize(cookie)
+        state = self.handler._get_value_from_macaroon(macaroon, "state")
+        nonce = self.handler._get_value_from_macaroon(macaroon, "nonce")
+        redirect = self.handler._get_value_from_macaroon(
+            macaroon, "client_redirect_url"
+        )
+
+        self.assertEqual(params["state"], [state])
+        self.assertEqual(params["nonce"], [nonce])
+        self.assertEqual(redirect, "http://client/redirect")
+
+    @defer.inlineCallbacks
+    def test_callback_error(self):
+        """Errors from the provider returned in the callback are displayed."""
+        self.handler._render_error = Mock()
+        request = Mock(args={})
+        request.args[b"error"] = [b"invalid_client"]
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("invalid_client", "")
+
+        request.args[b"error_description"] = [b"some description"]
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("invalid_client", "some description")
+
+    @defer.inlineCallbacks
+    def test_callback(self):
+        """Code callback works and display errors if something went wrong.
+
+        A lot of scenarios are tested here:
+         - when the callback works, with userinfo from ID token
+         - when the user mapping fails
+         - when ID token verification fails
+         - when the callback works, with userinfo fetched from the userinfo endpoint
+         - when the userinfo fetching fails
+         - when the code exchange fails
+        """
+        token = {
+            "type": "bearer",
+            "id_token": "id_token",
+            "access_token": "access_token",
+        }
+        userinfo = {
+            "sub": "foo",
+            "preferred_username": "bar",
+        }
+        user_id = UserID("foo", "domain.org")
+        self.handler._render_error = Mock(return_value=None)
+        self.handler._exchange_code = simple_async_mock(return_value=token)
+        self.handler._parse_id_token = simple_async_mock(return_value=userinfo)
+        self.handler._fetch_userinfo = simple_async_mock(return_value=userinfo)
+        self.handler._map_userinfo_to_user = simple_async_mock(return_value=user_id)
+        self.handler._auth_handler.complete_sso_login = simple_async_mock()
+        request = Mock(spec=["args", "getCookie", "addCookie"])
+
+        code = "code"
+        state = "state"
+        nonce = "nonce"
+        client_redirect_url = "http://client/redirect"
+        session = self.handler._generate_oidc_session_token(
+            state=state, nonce=nonce, client_redirect_url=client_redirect_url,
+        )
+        request.getCookie.return_value = session
+
+        request.args = {}
+        request.args[b"code"] = [code.encode("utf-8")]
+        request.args[b"state"] = [state.encode("utf-8")]
+
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+
+        self.handler._auth_handler.complete_sso_login.assert_called_once_with(
+            user_id, request, client_redirect_url,
+        )
+        self.handler._exchange_code.assert_called_once_with(code)
+        self.handler._parse_id_token.assert_called_once_with(token, nonce=nonce)
+        self.handler._map_userinfo_to_user.assert_called_once_with(userinfo, token)
+        self.handler._fetch_userinfo.assert_not_called()
+        self.handler._render_error.assert_not_called()
+
+        # Handle mapping errors
+        self.handler._map_userinfo_to_user = simple_async_mock(
+            raises=MappingException()
+        )
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("mapping_error")
+        self.handler._map_userinfo_to_user = simple_async_mock(return_value=user_id)
+
+        # Handle ID token errors
+        self.handler._parse_id_token = simple_async_mock(raises=Exception())
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("invalid_token")
+
+        self.handler._auth_handler.complete_sso_login.reset_mock()
+        self.handler._exchange_code.reset_mock()
+        self.handler._parse_id_token.reset_mock()
+        self.handler._map_userinfo_to_user.reset_mock()
+        self.handler._fetch_userinfo.reset_mock()
+
+        # With userinfo fetching
+        self.handler._scopes = []  # do not ask the "openid" scope
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+
+        self.handler._auth_handler.complete_sso_login.assert_called_once_with(
+            user_id, request, client_redirect_url,
+        )
+        self.handler._exchange_code.assert_called_once_with(code)
+        self.handler._parse_id_token.assert_not_called()
+        self.handler._map_userinfo_to_user.assert_called_once_with(userinfo, token)
+        self.handler._fetch_userinfo.assert_called_once_with(token)
+        self.handler._render_error.assert_not_called()
+
+        # Handle userinfo fetching error
+        self.handler._fetch_userinfo = simple_async_mock(raises=Exception())
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("fetch_error")
+
+        # Handle code exchange failure
+        self.handler._exchange_code = simple_async_mock(
+            raises=OidcError("invalid_request")
+        )
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("invalid_request")
+
+    @defer.inlineCallbacks
+    def test_callback_session(self):
+        """The callback verifies the session presence and validity"""
+        self.handler._render_error = Mock(return_value=None)
+        request = Mock(spec=["args", "getCookie", "addCookie"])
+
+        # Missing cookie
+        request.args = {}
+        request.getCookie.return_value = None
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("missing_session", "No session cookie found")
+
+        # Missing session parameter
+        request.args = {}
+        request.getCookie.return_value = "session"
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("invalid_request", "State parameter is missing")
+
+        # Invalid cookie
+        request.args = {}
+        request.args[b"state"] = [b"state"]
+        request.getCookie.return_value = "session"
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("invalid_session")
+
+        # Mismatching session
+        session = self.handler._generate_oidc_session_token(
+            state="state", nonce="nonce", client_redirect_url="http://client/redirect",
+        )
+        request.args = {}
+        request.args[b"state"] = [b"mismatching state"]
+        request.getCookie.return_value = session
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("mismatching_session")
+
+        # Valid session
+        request.args = {}
+        request.args[b"state"] = [b"state"]
+        request.getCookie.return_value = session
+        yield defer.ensureDeferred(self.handler.handle_oidc_callback(request))
+        self.assertRenderedError("invalid_request")
+
+    @override_config({"oidc_config": {"client_auth_method": "client_secret_post"}})
+    @defer.inlineCallbacks
+    def test_exchange_code(self):
+        """Code exchange behaves correctly and handles various error scenarios."""
+        token = {"type": "bearer"}
+        token_json = json.dumps(token).encode("utf-8")
+        self.http_client.request = simple_async_mock(
+            return_value=FakeResponse(code=200, phrase=b"OK", body=token_json)
+        )
+        code = "code"
+        ret = yield defer.ensureDeferred(self.handler._exchange_code(code))
+        kwargs = self.http_client.request.call_args[1]
+
+        self.assertEqual(ret, token)
+        self.assertEqual(kwargs["method"], "POST")
+        self.assertEqual(kwargs["uri"], TOKEN_ENDPOINT)
+
+        args = parse_qs(kwargs["data"].decode("utf-8"))
+        self.assertEqual(args["grant_type"], ["authorization_code"])
+        self.assertEqual(args["code"], [code])
+        self.assertEqual(args["client_id"], [CLIENT_ID])
+        self.assertEqual(args["client_secret"], [CLIENT_SECRET])
+        self.assertEqual(args["redirect_uri"], [CALLBACK_URL])
+
+        # Test error handling
+        self.http_client.request = simple_async_mock(
+            return_value=FakeResponse(
+                code=400,
+                phrase=b"Bad Request",
+                body=b'{"error": "foo", "error_description": "bar"}',
+            )
+        )
+        with self.assertRaises(OidcError) as exc:
+            yield defer.ensureDeferred(self.handler._exchange_code(code))
+        self.assertEqual(exc.exception.error, "foo")
+        self.assertEqual(exc.exception.error_description, "bar")
+
+        # Internal server error with no JSON body
+        self.http_client.request = simple_async_mock(
+            return_value=FakeResponse(
+                code=500, phrase=b"Internal Server Error", body=b"Not JSON",
+            )
+        )
+        with self.assertRaises(OidcError) as exc:
+            yield defer.ensureDeferred(self.handler._exchange_code(code))
+        self.assertEqual(exc.exception.error, "server_error")
+
+        # Internal server error with JSON body
+        self.http_client.request = simple_async_mock(
+            return_value=FakeResponse(
+                code=500,
+                phrase=b"Internal Server Error",
+                body=b'{"error": "internal_server_error"}',
+            )
+        )
+        with self.assertRaises(OidcError) as exc:
+            yield defer.ensureDeferred(self.handler._exchange_code(code))
+        self.assertEqual(exc.exception.error, "internal_server_error")
+
+        # 4xx error without "error" field
+        self.http_client.request = simple_async_mock(
+            return_value=FakeResponse(code=400, phrase=b"Bad request", body=b"{}",)
+        )
+        with self.assertRaises(OidcError) as exc:
+            yield defer.ensureDeferred(self.handler._exchange_code(code))
+        self.assertEqual(exc.exception.error, "server_error")
+
+        # 2xx error with "error" field
+        self.http_client.request = simple_async_mock(
+            return_value=FakeResponse(
+                code=200, phrase=b"OK", body=b'{"error": "some_error"}',
+            )
+        )
+        with self.assertRaises(OidcError) as exc:
+            yield defer.ensureDeferred(self.handler._exchange_code(code))
+        self.assertEqual(exc.exception.error, "some_error")
diff --git a/tox.ini b/tox.ini
index c699f3e46a..ad1902d47d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -185,6 +185,7 @@ commands = mypy \
             synapse/handlers/auth.py \
             synapse/handlers/cas_handler.py \
             synapse/handlers/directory.py \
+            synapse/handlers/oidc_handler.py \
             synapse/handlers/presence.py \
             synapse/handlers/saml_handler.py \
             synapse/handlers/sync.py \
-- 
cgit 1.5.1


From 66d03639dcc1d6b8cac849e334b17a7dbe558d18 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Thu, 14 May 2020 18:03:10 +0100
Subject: Notes on using git (#7496)

* general updates to CONTRIBUTING.md
* notes on updating your PR
* Notes on squash-merging or otherwise
* document git branching model
---
 CONTRIBUTING.md           | 171 ++++++++++++++++++++++++++++++----------------
 docs/dev/git.md           | 148 +++++++++++++++++++++++++++++++++++++++
 docs/dev/git/branches.jpg | Bin 0 -> 72228 bytes
 docs/dev/git/clean.png    | Bin 0 -> 110840 bytes
 docs/dev/git/squash.png   | Bin 0 -> 29667 bytes
 5 files changed, 261 insertions(+), 58 deletions(-)
 create mode 100644 docs/dev/git.md
 create mode 100644 docs/dev/git/branches.jpg
 create mode 100644 docs/dev/git/clean.png
 create mode 100644 docs/dev/git/squash.png

(limited to 'docs/dev')

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 253a0ca648..3350e533dc 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1,19 +1,20 @@
-# Contributing code to Matrix
+# Contributing code to Synapse
 
-Everyone is welcome to contribute code to Matrix
-(https://github.com/matrix-org), provided that they are willing to license
-their contributions under the same license as the project itself. We follow a
-simple 'inbound=outbound' model for contributions: the act of submitting an
-'inbound' contribution means that the contributor agrees to license the code
-under the same terms as the project's overall 'outbound' license - in our
-case, this is almost always Apache Software License v2 (see [LICENSE](LICENSE)).
+Everyone is welcome to contribute code to [matrix.org
+projects](https://github.com/matrix-org), provided that they are willing to
+license their contributions under the same license as the project itself. We
+follow a simple 'inbound=outbound' model for contributions: the act of
+submitting an 'inbound' contribution means that the contributor agrees to
+license the code under the same terms as the project's overall 'outbound'
+license - in our case, this is almost always Apache Software License v2 (see
+[LICENSE](LICENSE)).
 
 ## How to contribute
 
-The preferred and easiest way to contribute changes to Matrix is to fork the
-relevant project on github, and then [create a pull request](
-https://help.github.com/articles/using-pull-requests/) to ask us to pull
-your changes into our repo.
+The preferred and easiest way to contribute changes is to fork the relevant
+project on github, and then [create a pull request](
+https://help.github.com/articles/using-pull-requests/) to ask us to pull your
+changes into our repo.
 
 **The single biggest thing you need to know is: please base your changes on
 the develop branch - *not* master.**
@@ -28,35 +29,31 @@ use github's pull request workflow to review the contribution, and either ask
 you to make any refinements needed or merge it and make them ourselves. The
 changes will then land on master when we next do a release.
 
-We use [Buildkite](https://buildkite.com/matrix-dot-org/synapse) for continuous
-integration. If your change breaks the build, this will be shown in GitHub, so
-please keep an eye on the pull request for feedback.
+Some other things you will need to know when contributing to Synapse:
 
-To run unit tests in a local development environment, you can use:
+ * Please follow the [code style requirements](#code-style).
 
-- ``tox -e py35`` (requires tox to be installed by ``pip install tox``)
-  for SQLite-backed Synapse on Python 3.5.
-- ``tox -e py36`` for SQLite-backed Synapse on Python 3.6.
-- ``tox -e py36-postgres`` for PostgreSQL-backed Synapse on Python 3.6
-  (requires a running local PostgreSQL with access to create databases).
-- ``./test_postgresql.sh`` for PostgreSQL-backed Synapse on Python 3.5
-  (requires Docker). Entirely self-contained, recommended if you don't want to
-  set up PostgreSQL yourself.
+ * Please include a [changelog entry](#changelog) with each PR.
 
-Docker images are available for running the integration tests (SyTest) locally,
-see the [documentation in the SyTest repo](
-https://github.com/matrix-org/sytest/blob/develop/docker/README.md) for more
-information.
+ * Please [sign off](#sign-off) your contribution.
+
+ * Please keep an eye on the pull request for feedback from the [continuous
+   integration system](#continuous-integration-and-testing) and try to fix any
+   errors that come up.
+
+ * If you need to [update your PR](#updating-your-pull-request), just add new
+   commits to your branch rather than rebasing.
 
 ## Code style
 
-All Matrix projects have a well-defined code-style - and sometimes we've even
-got as far as documenting it... For instance, synapse's code style doc lives
-[here](docs/code_style.md).
+Synapse's code style is documented [here](docs/code_style.md). Please follow
+it, including the conventions for the [sample configuration
+file](docs/code_style.md#configuration-file-format).
 
-To facilitate meeting these criteria you can run `scripts-dev/lint.sh`
-locally. Since this runs the tools listed in the above document, you'll need
-python 3.6 and to install each tool:
+Many of the conventions are enforced by scripts which are run as part of the
+[continuous integration system](#continuous-integration-and-testing). To help
+check if you have followed the code style, you can run `scripts-dev/lint.sh`
+locally. You'll need python 3.6 or later, and to install a number of tools:
 
 ```
 # Install the dependencies
@@ -67,9 +64,11 @@ pip install -U black flake8 flake8-comprehensions isort
 ```
 
 **Note that the script does not just test/check, but also reformats code, so you
-may wish to ensure any new code is committed first**. By default this script
-checks all files and can take some time; if you alter only certain files, you
-might wish to specify paths as arguments to reduce the run-time:
+may wish to ensure any new code is committed first**.
+
+By default, this script checks all files and can take some time; if you alter
+only certain files, you might wish to specify paths as arguments to reduce the
+run-time:
 
 ```
 ./scripts-dev/lint.sh path/to/file1.py path/to/file2.py path/to/folder
@@ -82,7 +81,6 @@ Please ensure your changes match the cosmetic style of the existing project,
 and **never** mix cosmetic and functional changes in the same commit, as it
 makes it horribly hard to review otherwise.
 
-
 ## Changelog
 
 All changes, even minor ones, need a corresponding changelog / newsfragment
@@ -98,24 +96,55 @@ in the format of `PRnumber.type`. The type can be one of the following:
 * `removal` (also used for deprecations)
 * `misc` (for internal-only changes)
 
-The content of the file is your changelog entry, which should be a short
-description of your change in the same style as the rest of our [changelog](
-https://github.com/matrix-org/synapse/blob/master/CHANGES.md). The file can
-contain Markdown formatting, and should end with a full stop (.) or an
-exclamation mark (!) for consistency.
+This file will become part of our [changelog](
+https://github.com/matrix-org/synapse/blob/master/CHANGES.md) at the next
+release, so the content of the file should be a short description of your
+change in the same style as the rest of the changelog. The file can contain Markdown
+formatting, and should end with a full stop (.) or an exclamation mark (!) for
+consistency.
 
 Adding credits to the changelog is encouraged, we value your
 contributions and would like to have you shouted out in the release notes!
 
 For example, a fix in PR #1234 would have its changelog entry in
-`changelog.d/1234.bugfix`, and contain content like "The security levels of
-Florbs are now validated when received over federation. Contributed by Jane
-Matrix.".
+`changelog.d/1234.bugfix`, and contain content like:
+
+> The security levels of Florbs are now validated when received
+> via the `/federation/florb` endpoint. Contributed by Jane Matrix.
+
+If there are multiple pull requests involved in a single bugfix/feature/etc,
+then the content for each `changelog.d` file should be the same. Towncrier will
+merge the matching files together into a single changelog entry when we come to
+release.
+
+### How do I know what to call the changelog file before I create the PR?
+
+Obviously, you don't know if you should call your newsfile
+`1234.bugfix` or `5678.bugfix` until you create the PR, which leads to a
+chicken-and-egg problem.
+
+There are two options for solving this:
+
+ 1. Open the PR without a changelog file, see what number you got, and *then*
+    add the changelog file to your branch (see [Updating your pull
+    request](#updating-your-pull-request)), or:
 
-## Debian changelog
+ 1. Look at the [list of all
+    issues/PRs](https://github.com/matrix-org/synapse/issues?q=), add one to the
+    highest number you see, and quickly open the PR before somebody else claims
+    your number.
+
+    [This
+    script](https://github.com/richvdh/scripts/blob/master/next_github_number.sh)
+    might be helpful if you find yourself doing this a lot.
+
+Sorry, we know it's a bit fiddly, but it's *really* helpful for us when we come
+to put together a release!
+
+### Debian changelog
 
 Changes which affect the debian packaging files (in `debian`) are an
-exception.
+exception to the rule that all changes require a `changelog.d` file.
 
 In this case, you will need to add an entry to the debian changelog for the
 next release. For this, run the following command:
@@ -200,19 +229,45 @@ Git allows you to add this signoff automatically when using the `-s`
 flag to `git commit`, which uses the name and email set in your
 `user.name` and `user.email` git configs.
 
-## Merge Strategy
+## Continuous integration and testing
+
+[Buildkite](https://buildkite.com/matrix-dot-org/synapse) will automatically
+run a series of checks and tests against any PR which is opened against the
+project; if your change breaks the build, this will be shown in GitHub, with
+links to the build results. If your build fails, please try to fix the errors
+and update your branch.
+
+To run unit tests in a local development environment, you can use:
+
+- ``tox -e py35`` (requires tox to be installed by ``pip install tox``)
+  for SQLite-backed Synapse on Python 3.5.
+- ``tox -e py36`` for SQLite-backed Synapse on Python 3.6.
+- ``tox -e py36-postgres`` for PostgreSQL-backed Synapse on Python 3.6
+  (requires a running local PostgreSQL with access to create databases).
+- ``./test_postgresql.sh`` for PostgreSQL-backed Synapse on Python 3.5
+  (requires Docker). Entirely self-contained, recommended if you don't want to
+  set up PostgreSQL yourself.
+
+Docker images are available for running the integration tests (SyTest) locally,
+see the [documentation in the SyTest repo](
+https://github.com/matrix-org/sytest/blob/develop/docker/README.md) for more
+information.
+
+## Updating your pull request
+
+If you decide to make changes to your pull request - perhaps to address issues
+raised in a review, or to fix problems highlighted by [continuous
+integration](#continuous-integration-and-testing) - just add new commits to your
+branch, and push to GitHub. The pull request will automatically be updated.
 
-We use the commit history of develop/master extensively to identify
-when regressions were introduced and what changes have been made.
+Please **avoid** rebasing your branch, especially once the PR has been
+reviewed: doing so makes it very difficult for a reviewer to see what has
+changed since a previous review.
 
-We aim to have a clean merge history, which means we normally squash-merge
-changes into develop. For small changes this means there is no need to rebase
-to clean up your PR before merging. Larger changes with an organised set of
-commits may be merged as-is, if the history is judged to be useful.
+## Notes for maintainers on merging PRs etc
 
-This use of squash-merging will mean PRs built on each other will be hard to 
-merge. We suggest avoiding these where possible, and if required, ensuring
-each PR has a tidy set of commits to ease merging.
+There are some notes for those with commit access to the project on how we
+manage git [here](docs/dev/git.md).
 
 ## Conclusion
 
diff --git a/docs/dev/git.md b/docs/dev/git.md
new file mode 100644
index 0000000000..b747ff20c9
--- /dev/null
+++ b/docs/dev/git.md
@@ -0,0 +1,148 @@
+Some notes on how we use git
+============================
+
+On keeping the commit history clean
+-----------------------------------
+
+In an ideal world, our git commit history would be a linear progression of
+commits each of which contains a single change building on what came
+before. Here, by way of an arbitrary example, is the top of `git log --graph
+b2dba0607`:
+
+<img src="git/clean.png" alt="clean git graph" width="500px">
+
+Note how the commit comment explains clearly what is changing and why. Also
+note the *absence* of merge commits, as well as the absence of commits called
+things like (to pick a few culprits):
+[“pep8”](https://github.com/matrix-org/synapse/commit/84691da6c), [“fix broken
+test”](https://github.com/matrix-org/synapse/commit/474810d9d),
+[“oops”](https://github.com/matrix-org/synapse/commit/c9d72e457),
+[“typo”](https://github.com/matrix-org/synapse/commit/836358823), or [“Who's
+the president?”](https://github.com/matrix-org/synapse/commit/707374d5d).
+
+There are a number of reasons why keeping a clean commit history is a good
+thing:
+
+ * From time to time, after a change lands, it turns out to be necessary to
+   revert it, or to backport it to a release branch. Those operations are
+   *much* easier when the change is contained in a single commit.
+
+ * Similarly, it's much easier to answer questions like “is the fix for
+   `/publicRooms` on the release branch?” if that change consists of a single
+   commit.
+
+ * Likewise: “what has changed on this branch in the last week?” is much
+   clearer without merges and “pep8” commits everywhere.
+
+ * Sometimes we need to figure out where a bug got introduced, or some
+   behaviour changed. One way of doing that is with `git bisect`: pick an
+   arbitrary commit between the known good point and the known bad point, and
+   see how the code behaves. However, that strategy fails if the commit you
+   chose is the middle of someone's epic branch in which they broke the world
+   before putting it back together again.
+
+One counterargument is that it is sometimes useful to see how a PR evolved as
+it went through review cycles. This is true, but that information is always
+available via the GitHub UI (or via the little-known [refs/pull
+namespace](https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/checking-out-pull-requests-locally)).
+
+
+Of course, in reality, things are more complicated than that. We have release
+branches as well as `develop` and `master`, and we deliberately merge changes
+between them. Bugs often slip through and have to be fixed later. That's all
+fine: this not a cast-iron rule which must be obeyed, but an ideal to aim
+towards.
+
+Merges, squashes, rebases: wtf?
+-------------------------------
+
+Ok, so that's what we'd like to achieve. How do we achieve it?
+
+The TL;DR is: when you come to merge a pull request, you *probably* want to
+“squash and merge”:
+
+![squash and merge](git/squash.png).
+
+(This applies whether you are merging your own PR, or that of another
+contributor.)
+
+“Squash and merge”<sup id="a1">[1](#f1)</sup> takes all of the changes in the
+PR, and bundles them into a single commit. GitHub gives you the opportunity to
+edit the commit message before you confirm, and normally you should do so,
+because the default will be useless (again: `* woops typo` is not a useful
+thing to keep in the historical record).
+
+The main problem with this approach comes when you have a series of pull
+requests which build on top of one another: as soon as you squash-merge the
+first PR, you'll end up with a stack of conflicts to resolve in all of the
+others. In general, it's best to avoid this situation in the first place by
+trying not to have multiple related PRs in flight at the same time. Still,
+sometimes that's not possible and doing a regular merge is the lesser evil.
+
+Another occasion in which a regular merge makes more sense is a PR where you've
+deliberately created a series of commits each of which makes sense in its own
+right. For example: [a PR which gradually propagates a refactoring operation
+through the codebase](https://github.com/matrix-org/synapse/pull/6837), or [a
+PR which is the culmination of several other
+PRs](https://github.com/matrix-org/synapse/pull/5987). In this case the ability
+to figure out when a particular change/bug was introduced could be very useful.
+
+Ultimately: **this is not a hard-and-fast-rule**. If in doubt, ask yourself “do
+each of the commits I am about to merge make sense in their own right”, but
+remember that we're just doing our best to balance “keeping the commit history
+clean” with other factors.
+
+Git branching model
+-------------------
+
+A [lot](https://nvie.com/posts/a-successful-git-branching-model/)
+[of](http://scottchacon.com/2011/08/31/github-flow.html)
+[words](https://www.endoflineblog.com/gitflow-considered-harmful) have been
+written in the past about git branching models (no really, [a
+lot](https://martinfowler.com/articles/branching-patterns.html)). I tend to
+think the whole thing is overblown. Fundamentally, it's not that
+complicated. Here's how we do it.
+
+Let's start with a picture:
+
+![branching model](git/branches.jpg)
+
+It looks complicated, but it's really not. There's one basic rule: *anyone* is
+free to merge from *any* more-stable branch to *any* less-stable branch at
+*any* time<sup id="a2">[2](#f2)</sup>. (The principle behind this is that if a
+change is good enough for the more-stable branch, then it's also good enough go
+put in a less-stable branch.)
+
+Meanwhile, merging (or squashing, as per the above) from a less-stable to a
+more-stable branch is a deliberate action in which you want to publish a change
+or a set of changes to (some subset of) the world: for example, this happens
+when a PR is landed, or as part of our release process.
+
+So, what counts as a more- or less-stable branch? A little reflection will show
+that our active branches are ordered thus, from more-stable to less-stable:
+
+ * `master` (tracks our last release).
+ * `release-vX.Y.Z` (the branch where we prepare the next release)<sup
+   id="a3">[3](#f3)</sup>.
+ * PR branches which are targeting the release.
+ * `develop` (our "mainline" branch containing our bleeding-edge).
+ * regular PR branches.
+
+The corollary is: if you have a bugfix that needs to land in both
+`release-vX.Y.Z` *and* `develop`, then you should base your PR on
+`release-vX.Y.Z`, get it merged there, and then merge from `release-vX.Y.Z` to
+`develop`. (If a fix lands in `develop` and we later need it in a
+release-branch, we can of course cherry-pick it, but landing it in the release
+branch first helps reduce the chance of annoying conflicts.)
+
+---
+
+<b id="f1">[1]</b>: “Squash and merge” is GitHub's term for this
+operation. Given that there is no merge involved, I'm not convinced it's the
+most intuitive name. [^](#a1)
+
+<b id="f2">[2]</b>: Well, anyone with commit access.[^](#a2)
+
+<b id="f3">[3]</b>: Very, very occasionally (I think this has happened once in
+the history of Synapse), we've had two releases in flight at once. Obviously,
+`release-v1.2.3` is more-stable than `release-v1.3.0`. [^](#a3)
diff --git a/docs/dev/git/branches.jpg b/docs/dev/git/branches.jpg
new file mode 100644
index 0000000000..715ecc8cd0
Binary files /dev/null and b/docs/dev/git/branches.jpg differ
diff --git a/docs/dev/git/clean.png b/docs/dev/git/clean.png
new file mode 100644
index 0000000000..3accd7ccef
Binary files /dev/null and b/docs/dev/git/clean.png differ
diff --git a/docs/dev/git/squash.png b/docs/dev/git/squash.png
new file mode 100644
index 0000000000..234caca3e4
Binary files /dev/null and b/docs/dev/git/squash.png differ
-- 
cgit 1.5.1


From 11de843626fa3a7e54060d4fafee5bcaa0f637a4 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Wed, 3 Jun 2020 21:13:17 +0100
Subject: Cleanups to the OpenID Connect integration (#7628)

docs, default configs, comments. Nothing very significant.
---
 changelog.d/7628.misc            |   1 +
 docs/dev/oidc.md                 | 175 ---------------------------------
 docs/openid.md                   | 206 +++++++++++++++++++++++++++++++++++++++
 docs/sample_config.yaml          | 162 +++++++++++++++++-------------
 synapse/config/oidc_config.py    | 176 +++++++++++++++++++--------------
 synapse/config/saml2_config.py   |   2 +
 synapse/config/sso.py            |   3 +-
 synapse/handlers/oidc_handler.py |  27 +++--
 8 files changed, 428 insertions(+), 324 deletions(-)
 create mode 100644 changelog.d/7628.misc
 delete mode 100644 docs/dev/oidc.md
 create mode 100644 docs/openid.md

(limited to 'docs/dev')

diff --git a/changelog.d/7628.misc b/changelog.d/7628.misc
new file mode 100644
index 0000000000..74007450fb
--- /dev/null
+++ b/changelog.d/7628.misc
@@ -0,0 +1 @@
+Minor cleanups to OpenID Connect integration.
diff --git a/docs/dev/oidc.md b/docs/dev/oidc.md
deleted file mode 100644
index a90c5d2441..0000000000
--- a/docs/dev/oidc.md
+++ /dev/null
@@ -1,175 +0,0 @@
-# How to test OpenID Connect
-
-Any OpenID Connect Provider (OP) should work with Synapse, as long as it supports the authorization code flow.
-There are a few options for that:
-
- - start a local OP. Synapse has been tested with [Hydra][hydra] and [Dex][dex-idp].
-   Note that for an OP to work, it should be served under a secure (HTTPS) origin.
-   A certificate signed with a self-signed, locally trusted CA should work. In that case, start Synapse with a `SSL_CERT_FILE` environment variable set to the path of the CA.
- - use a publicly available OP. Synapse has been tested with [Google][google-idp].
- - setup a SaaS OP, like [Auth0][auth0] and [Okta][okta]. Auth0 has a free tier which has been tested with Synapse.
-
-[google-idp]: https://developers.google.com/identity/protocols/OpenIDConnect#authenticatingtheuser
-[auth0]: https://auth0.com/
-[okta]: https://www.okta.com/
-[dex-idp]: https://github.com/dexidp/dex
-[hydra]: https://www.ory.sh/docs/hydra/
-
-
-## Sample configs
-
-Here are a few configs for providers that should work with Synapse.
-
-### [Dex][dex-idp]
-
-[Dex][dex-idp] is a simple, open-source, certified OpenID Connect Provider.
-Although it is designed to help building a full-blown provider, with some external database, it can be configured with static passwords in a config file.
-
-Follow the [Getting Started guide](https://github.com/dexidp/dex/blob/master/Documentation/getting-started.md) to install Dex.
-
-Edit `examples/config-dev.yaml` config file from the Dex repo to add a client:
-
-```yaml
-staticClients:
-- id: synapse
-  secret: secret
-  redirectURIs:
-  - '[synapse base url]/_synapse/oidc/callback'
-  name: 'Synapse'
-```
-
-Run with `dex serve examples/config-dex.yaml`
-
-Synapse config:
-
-```yaml
-oidc_config:
-   enabled: true
-   skip_verification: true # This is needed as Dex is served on an insecure endpoint
-   issuer: "http://127.0.0.1:5556/dex"
-   discover: true
-   client_id: "synapse"
-   client_secret: "secret"
-   scopes:
-     - openid
-     - profile
-   user_mapping_provider:
-     config:
-       localpart_template: '{{ user.name }}'
-       display_name_template: '{{ user.name|capitalize }}'
-```
-
-### [Auth0][auth0]
-
-1. Create a regular web application for Synapse
-2. Set the Allowed Callback URLs to `[synapse base url]/_synapse/oidc/callback`
-3. Add a rule to add the `preferred_username` claim.
-   <details>
-    <summary>Code sample</summary>
-
-    ```js
-    function addPersistenceAttribute(user, context, callback) {
-      user.user_metadata = user.user_metadata || {};
-      user.user_metadata.preferred_username = user.user_metadata.preferred_username || user.user_id;
-      context.idToken.preferred_username = user.user_metadata.preferred_username;
-
-      auth0.users.updateUserMetadata(user.user_id, user.user_metadata)
-        .then(function(){
-            callback(null, user, context);
-        })
-        .catch(function(err){
-            callback(err);
-        });
-    }
-    ```
-
-  </details>
-
-
-```yaml
-oidc_config:
-   enabled: true
-   issuer: "https://your-tier.eu.auth0.com/" # TO BE FILLED
-   discover: true
-   client_id: "your-client-id" # TO BE FILLED
-   client_secret: "your-client-secret" # TO BE FILLED
-   scopes:
-     - openid
-     - profile
-   user_mapping_provider:
-     config:
-       localpart_template: '{{ user.preferred_username }}'
-       display_name_template: '{{ user.name }}'
-```
-
-### GitHub
-
-GitHub is a bit special as it is not an OpenID Connect compliant provider, but just a regular OAuth2 provider.
-The `/user` API endpoint can be used to retrieve informations from the user.
-As the OIDC login mechanism needs an attribute to uniquely identify users and that endpoint does not return a `sub` property, an alternative `subject_claim` has to be set.
-
-1. Create a new OAuth application: https://github.com/settings/applications/new
-2. Set the callback URL to `[synapse base url]/_synapse/oidc/callback`
-
-```yaml
-oidc_config:
-   enabled: true
-   issuer: "https://github.com/"
-   discover: false
-   client_id: "your-client-id" # TO BE FILLED
-   client_secret: "your-client-secret" # TO BE FILLED
-   authorization_endpoint: "https://github.com/login/oauth/authorize"
-   token_endpoint: "https://github.com/login/oauth/access_token"
-   userinfo_endpoint: "https://api.github.com/user"
-   scopes:
-     - read:user
-   user_mapping_provider:
-     config:
-       subject_claim: 'id'
-       localpart_template: '{{ user.login }}'
-       display_name_template: '{{ user.name }}'
-```
-
-### Google
-
-1. Setup a project in the Google API Console
-2. Obtain the OAuth 2.0 credentials (see <https://developers.google.com/identity/protocols/oauth2/openid-connect>)
-3. Add this Authorized redirect URI: `[synapse base url]/_synapse/oidc/callback`
-
-```yaml
-oidc_config:
-   enabled: true
-   issuer: "https://accounts.google.com/"
-   discover: true
-   client_id: "your-client-id" # TO BE FILLED
-   client_secret: "your-client-secret" # TO BE FILLED
-   scopes:
-     - openid
-     - profile
-   user_mapping_provider:
-     config:
-       localpart_template: '{{ user.given_name|lower }}'
-       display_name_template: '{{ user.name }}'
-```
-
-### Twitch
-
-1. Setup a developer account on [Twitch](https://dev.twitch.tv/)
-2. Obtain the OAuth 2.0 credentials by [creating an app](https://dev.twitch.tv/console/apps/)
-3. Add this OAuth Redirect URL: `[synapse base url]/_synapse/oidc/callback`
-
-```yaml
-oidc_config:
-   enabled: true
-   issuer: "https://id.twitch.tv/oauth2/"
-   discover: true
-   client_id: "your-client-id" # TO BE FILLED
-   client_secret: "your-client-secret" # TO BE FILLED
-   client_auth_method: "client_secret_post"
-   scopes:
-     - openid
-   user_mapping_provider:
-     config:
-       localpart_template: '{{ user.preferred_username }}'
-       display_name_template: '{{ user.name }}'
-```
diff --git a/docs/openid.md b/docs/openid.md
new file mode 100644
index 0000000000..688379ddd9
--- /dev/null
+++ b/docs/openid.md
@@ -0,0 +1,206 @@
+# Configuring Synapse to authenticate against an OpenID Connect provider
+
+Synapse can be configured to use an OpenID Connect Provider (OP) for
+authentication, instead of its own local password database.
+
+Any OP should work with Synapse, as long as it supports the authorization code
+flow. There are a few options for that:
+
+ - start a local OP. Synapse has been tested with [Hydra][hydra] and
+   [Dex][dex-idp].  Note that for an OP to work, it should be served under a
+   secure (HTTPS) origin.  A certificate signed with a self-signed, locally
+   trusted CA should work. In that case, start Synapse with a `SSL_CERT_FILE`
+   environment variable set to the path of the CA.
+
+ - set up a SaaS OP, like [Google][google-idp], [Auth0][auth0] or
+   [Okta][okta]. Synapse has been tested with Auth0 and Google.
+
+It may also be possible to use other OAuth2 providers which provide the
+[authorization code grant type](https://tools.ietf.org/html/rfc6749#section-4.1),
+such as [Github][github-idp].
+
+[google-idp]: https://developers.google.com/identity/protocols/oauth2/openid-connect
+[auth0]: https://auth0.com/
+[okta]: https://www.okta.com/
+[dex-idp]: https://github.com/dexidp/dex
+[hydra]: https://www.ory.sh/docs/hydra/
+[github-idp]: https://developer.github.com/apps/building-oauth-apps/authorizing-oauth-apps
+
+## Preparing Synapse
+
+The OpenID integration in Synapse uses the
+[`authlib`](https://pypi.org/project/Authlib/) library, which must be installed
+as follows:
+
+ * The relevant libraries are included in the Docker images and Debian packages
+   provided by `matrix.org` so no further action is needed.
+
+ * If you installed Synapse into a virtualenv, run `/path/to/env/bin/pip
+   install synapse[oidc]` to install the necessary dependencies.
+
+ * For other installation mechanisms, see the documentation provided by the
+   maintainer.
+
+To enable the OpenID integration, you should then add an `oidc_config` section
+to your configuration file (or uncomment the `enabled: true` line in the
+existing section). See [sample_config.yaml](./sample_config.yaml) for some
+sample settings, as well as the text below for example configurations for
+specific providers.
+
+## Sample configs
+
+Here are a few configs for providers that should work with Synapse.
+
+### [Dex][dex-idp]
+
+[Dex][dex-idp] is a simple, open-source, certified OpenID Connect Provider.
+Although it is designed to help building a full-blown provider with an
+external database, it can be configured with static passwords in a config file.
+
+Follow the [Getting Started
+guide](https://github.com/dexidp/dex/blob/master/Documentation/getting-started.md)
+to install Dex.
+
+Edit `examples/config-dev.yaml` config file from the Dex repo to add a client:
+
+```yaml
+staticClients:
+- id: synapse
+  secret: secret
+  redirectURIs:
+  - '[synapse public baseurl]/_synapse/oidc/callback'
+  name: 'Synapse'
+```
+
+Run with `dex serve examples/config-dex.yaml`.
+
+Synapse config:
+
+```yaml
+oidc_config:
+   enabled: true
+   skip_verification: true # This is needed as Dex is served on an insecure endpoint
+   issuer: "http://127.0.0.1:5556/dex"
+   client_id: "synapse"
+   client_secret: "secret"
+   scopes: ["openid", "profile"]
+   user_mapping_provider:
+     config:
+       localpart_template: "{{ user.name }}"
+       display_name_template: "{{ user.name|capitalize }}"
+```
+
+### [Auth0][auth0]
+
+1. Create a regular web application for Synapse
+2. Set the Allowed Callback URLs to `[synapse public baseurl]/_synapse/oidc/callback`
+3. Add a rule to add the `preferred_username` claim.
+   <details>
+    <summary>Code sample</summary>
+
+    ```js
+    function addPersistenceAttribute(user, context, callback) {
+      user.user_metadata = user.user_metadata || {};
+      user.user_metadata.preferred_username = user.user_metadata.preferred_username || user.user_id;
+      context.idToken.preferred_username = user.user_metadata.preferred_username;
+
+      auth0.users.updateUserMetadata(user.user_id, user.user_metadata)
+        .then(function(){
+            callback(null, user, context);
+        })
+        .catch(function(err){
+            callback(err);
+        });
+    }
+    ```
+  </details>
+
+Synapse config:
+
+```yaml
+oidc_config:
+   enabled: true
+   issuer: "https://your-tier.eu.auth0.com/" # TO BE FILLED
+   client_id: "your-client-id" # TO BE FILLED
+   client_secret: "your-client-secret" # TO BE FILLED
+   scopes: ["openid", "profile"]
+   user_mapping_provider:
+     config:
+       localpart_template: "{{ user.preferred_username }}"
+       display_name_template: "{{ user.name }}"
+```
+
+### GitHub
+
+GitHub is a bit special as it is not an OpenID Connect compliant provider, but
+just a regular OAuth2 provider.
+
+The [`/user` API endpoint](https://developer.github.com/v3/users/#get-the-authenticated-user)
+can be used to retrieve information on the authenticated user. As the Synaspse
+login mechanism needs an attribute to uniquely identify users, and that endpoint
+does not return a `sub` property, an alternative `subject_claim` has to be set.
+
+1. Create a new OAuth application: https://github.com/settings/applications/new.
+2. Set the callback URL to `[synapse public baseurl]/_synapse/oidc/callback`.
+
+Synapse config:
+
+```yaml
+oidc_config:
+   enabled: true
+   discover: false
+   issuer: "https://github.com/"
+   client_id: "your-client-id" # TO BE FILLED
+   client_secret: "your-client-secret" # TO BE FILLED
+   authorization_endpoint: "https://github.com/login/oauth/authorize"
+   token_endpoint: "https://github.com/login/oauth/access_token"
+   userinfo_endpoint: "https://api.github.com/user"
+   scopes: ["read:user"]
+   user_mapping_provider:
+     config:
+       subject_claim: "id"
+       localpart_template: "{{ user.login }}"
+       display_name_template: "{{ user.name }}"
+```
+
+### [Google][google-idp]
+
+1. Set up a project in the Google API Console (see
+   https://developers.google.com/identity/protocols/oauth2/openid-connect#appsetup).
+2. add an "OAuth Client ID" for a Web Application under "Credentials".
+3. Copy the Client ID and Client Secret, and add the following to your synapse config:
+   ```yaml
+   oidc_config:
+     enabled: true
+     issuer: "https://accounts.google.com/"
+     client_id: "your-client-id" # TO BE FILLED
+     client_secret: "your-client-secret" # TO BE FILLED
+     scopes: ["openid", "profile"]
+     user_mapping_provider:
+       config:
+         localpart_template: "{{ user.given_name|lower }}"
+         display_name_template: "{{ user.name }}"
+   ```
+4. Back in the Google console, add this Authorized redirect URI: `[synapse
+   public baseurl]/_synapse/oidc/callback`.
+
+### Twitch
+
+1. Setup a developer account on [Twitch](https://dev.twitch.tv/)
+2. Obtain the OAuth 2.0 credentials by [creating an app](https://dev.twitch.tv/console/apps/)
+3. Add this OAuth Redirect URL: `[synapse public baseurl]/_synapse/oidc/callback`
+
+Synapse config:
+
+```yaml
+oidc_config:
+   enabled: true
+   issuer: "https://id.twitch.tv/oauth2/"
+   client_id: "your-client-id" # TO BE FILLED
+   client_secret: "your-client-secret" # TO BE FILLED
+   client_auth_method: "client_secret_post"
+   user_mapping_provider:
+     config:
+       localpart_template: '{{ user.preferred_username }}'
+       display_name_template: '{{ user.name }}'
+```
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index 6784234d5f..b06394a2bd 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -1379,6 +1379,8 @@ trusted_key_servers:
 #key_server_signing_keys_path: "key_server_signing_keys.key"
 
 
+## Single sign-on integration ##
+
 # Enable SAML2 for registration and login. Uses pysaml2.
 #
 # At least one of `sp_config` or `config_path` must be set in this section to
@@ -1526,92 +1528,119 @@ saml2_config:
   #template_dir: "res/templates"
 
 
-# Enable OpenID Connect for registration and login. Uses authlib.
+# OpenID Connect integration. The following settings can be used to make Synapse
+# use an OpenID Connect Provider for authentication, instead of its internal
+# password database.
+#
+# See https://github.com/matrix-org/synapse/blob/master/openid.md.
 #
 oidc_config:
-    # enable OpenID Connect. Defaults to false.
-    #
-    #enabled: true
+  # Uncomment the following to enable authorization against an OpenID Connect
+  # server. Defaults to false.
+  #
+  #enabled: true
 
-    # use the OIDC discovery mechanism to discover endpoints. Defaults to true.
-    #
-    #discover: true
+  # Uncomment the following to disable use of the OIDC discovery mechanism to
+  # discover endpoints. Defaults to true.
+  #
+  #discover: false
 
-    # the OIDC issuer. Used to validate tokens and discover the providers endpoints. Required.
-    #
-    #issuer: "https://accounts.example.com/"
+  # the OIDC issuer. Used to validate tokens and (if discovery is enabled) to
+  # discover the provider's endpoints.
+  #
+  # Required if 'enabled' is true.
+  #
+  #issuer: "https://accounts.example.com/"
 
-    # oauth2 client id to use. Required.
-    #
-    #client_id: "provided-by-your-issuer"
+  # oauth2 client id to use.
+  #
+  # Required if 'enabled' is true.
+  #
+  #client_id: "provided-by-your-issuer"
 
-    # oauth2 client secret to use. Required.
-    #
-    #client_secret: "provided-by-your-issuer"
+  # oauth2 client secret to use.
+  #
+  # Required if 'enabled' is true.
+  #
+  #client_secret: "provided-by-your-issuer"
 
-    # auth method to use when exchanging the token.
-    # Valid values are "client_secret_basic" (default), "client_secret_post" and "none".
-    #
-    #client_auth_method: "client_secret_basic"
+  # auth method to use when exchanging the token.
+  # Valid values are 'client_secret_basic' (default), 'client_secret_post' and
+  # 'none'.
+  #
+  #client_auth_method: client_secret_post
 
-    # list of scopes to ask. This should include the "openid" scope. Defaults to ["openid"].
-    #
-    #scopes: ["openid"]
+  # list of scopes to request. This should normally include the "openid" scope.
+  # Defaults to ["openid"].
+  #
+  #scopes: ["openid", "profile"]
 
-    # the oauth2 authorization endpoint. Required if provider discovery is disabled.
-    #
-    #authorization_endpoint: "https://accounts.example.com/oauth2/auth"
+  # the oauth2 authorization endpoint. Required if provider discovery is disabled.
+  #
+  #authorization_endpoint: "https://accounts.example.com/oauth2/auth"
 
-    # the oauth2 token endpoint. Required if provider discovery is disabled.
-    #
-    #token_endpoint: "https://accounts.example.com/oauth2/token"
+  # the oauth2 token endpoint. Required if provider discovery is disabled.
+  #
+  #token_endpoint: "https://accounts.example.com/oauth2/token"
 
-    # the OIDC userinfo endpoint. Required if discovery is disabled and the "openid" scope is not asked.
-    #
-    #userinfo_endpoint: "https://accounts.example.com/userinfo"
+  # the OIDC userinfo endpoint. Required if discovery is disabled and the
+  # "openid" scope is not requested.
+  #
+  #userinfo_endpoint: "https://accounts.example.com/userinfo"
 
-    # URI where to fetch the JWKS. Required if discovery is disabled and the "openid" scope is used.
-    #
-    #jwks_uri: "https://accounts.example.com/.well-known/jwks.json"
+  # URI where to fetch the JWKS. Required if discovery is disabled and the
+  # "openid" scope is used.
+  #
+  #jwks_uri: "https://accounts.example.com/.well-known/jwks.json"
 
-    # skip metadata verification. Defaults to false.
-    # Use this if you are connecting to a provider that is not OpenID Connect compliant.
-    # Avoid this in production.
-    #
-    #skip_verification: false
+  # Uncomment to skip metadata verification. Defaults to false.
+  #
+  # Use this if you are connecting to a provider that is not OpenID Connect
+  # compliant.
+  # Avoid this in production.
+  #
+  #skip_verification: true
 
+  # An external module can be provided here as a custom solution to mapping
+  # attributes returned from a OIDC provider onto a matrix user.
+  #
+  user_mapping_provider:
+    # The custom module's class. Uncomment to use a custom module.
+    # Default is 'synapse.handlers.oidc_handler.JinjaOidcMappingProvider'.
+    #
+    # See https://github.com/matrix-org/synapse/blob/master/docs/sso_mapping_providers.md#openid-mapping-providers
+    # for information on implementing a custom mapping provider.
+    #
+    #module: mapping_provider.OidcMappingProvider
 
-    # An external module can be provided here as a custom solution to mapping
-    # attributes returned from a OIDC provider onto a matrix user.
+    # Custom configuration values for the module. This section will be passed as
+    # a Python dictionary to the user mapping provider module's `parse_config`
+    # method.
+    #
+    # The examples below are intended for the default provider: they should be
+    # changed if using a custom provider.
     #
-    user_mapping_provider:
-      # The custom module's class. Uncomment to use a custom module.
-      # Default is 'synapse.handlers.oidc_handler.JinjaOidcMappingProvider'.
+    config:
+      # name of the claim containing a unique identifier for the user.
+      # Defaults to `sub`, which OpenID Connect compliant providers should provide.
       #
-      #module: mapping_provider.OidcMappingProvider
+      #subject_claim: "sub"
 
-      # Custom configuration values for the module. Below options are intended
-      # for the built-in provider, they should be changed if using a custom
-      # module. This section will be passed as a Python dictionary to the
-      # module's `parse_config` method.
+      # Jinja2 template for the localpart of the MXID.
       #
-      # Below is the config of the default mapping provider, based on Jinja2
-      # templates. Those templates are used to render user attributes, where the
-      # userinfo object is available through the `user` variable.
+      # When rendering, this template is given the following variables:
+      #   * user: The claims returned by the UserInfo Endpoint and/or in the ID
+      #     Token
       #
-      config:
-        # name of the claim containing a unique identifier for the user.
-        # Defaults to `sub`, which OpenID Connect compliant providers should provide.
-        #
-        #subject_claim: "sub"
-
-        # Jinja2 template for the localpart of the MXID
-        #
-        localpart_template: "{{ user.preferred_username }}"
+      # This must be configured if using the default mapping provider.
+      #
+      localpart_template: "{{ user.preferred_username }}"
 
-        # Jinja2 template for the display name to set on first login. Optional.
-        #
-        #display_name_template: "{{ user.given_name }} {{ user.last_name }}"
+      # Jinja2 template for the display name to set on first login.
+      #
+      # If unset, no displayname will be set.
+      #
+      #display_name_template: "{{ user.given_name }} {{ user.last_name }}"
 
 
 
@@ -1626,7 +1655,8 @@ oidc_config:
 #   #    name: value
 
 
-# Additional settings to use with single-sign on systems such as SAML2 and CAS.
+# Additional settings to use with single-sign on systems such as OpenID Connect,
+# SAML2 and CAS.
 #
 sso:
     # A list of client URLs which are whitelisted so that the user does not
diff --git a/synapse/config/oidc_config.py b/synapse/config/oidc_config.py
index 586038078f..e24dd637bc 100644
--- a/synapse/config/oidc_config.py
+++ b/synapse/config/oidc_config.py
@@ -55,7 +55,6 @@ class OIDCConfig(Config):
         self.oidc_token_endpoint = oidc_config.get("token_endpoint")
         self.oidc_userinfo_endpoint = oidc_config.get("userinfo_endpoint")
         self.oidc_jwks_uri = oidc_config.get("jwks_uri")
-        self.oidc_subject_claim = oidc_config.get("subject_claim", "sub")
         self.oidc_skip_verification = oidc_config.get("skip_verification", False)
 
         ump_config = oidc_config.get("user_mapping_provider", {})
@@ -86,92 +85,119 @@ class OIDCConfig(Config):
 
     def generate_config_section(self, config_dir_path, server_name, **kwargs):
         return """\
-        # Enable OpenID Connect for registration and login. Uses authlib.
+        # OpenID Connect integration. The following settings can be used to make Synapse
+        # use an OpenID Connect Provider for authentication, instead of its internal
+        # password database.
+        #
+        # See https://github.com/matrix-org/synapse/blob/master/openid.md.
         #
         oidc_config:
-            # enable OpenID Connect. Defaults to false.
-            #
-            #enabled: true
-
-            # use the OIDC discovery mechanism to discover endpoints. Defaults to true.
-            #
-            #discover: true
-
-            # the OIDC issuer. Used to validate tokens and discover the providers endpoints. Required.
-            #
-            #issuer: "https://accounts.example.com/"
-
-            # oauth2 client id to use. Required.
-            #
-            #client_id: "provided-by-your-issuer"
-
-            # oauth2 client secret to use. Required.
-            #
-            #client_secret: "provided-by-your-issuer"
-
-            # auth method to use when exchanging the token.
-            # Valid values are "client_secret_basic" (default), "client_secret_post" and "none".
-            #
-            #client_auth_method: "client_secret_basic"
-
-            # list of scopes to ask. This should include the "openid" scope. Defaults to ["openid"].
-            #
-            #scopes: ["openid"]
-
-            # the oauth2 authorization endpoint. Required if provider discovery is disabled.
+          # Uncomment the following to enable authorization against an OpenID Connect
+          # server. Defaults to false.
+          #
+          #enabled: true
+
+          # Uncomment the following to disable use of the OIDC discovery mechanism to
+          # discover endpoints. Defaults to true.
+          #
+          #discover: false
+
+          # the OIDC issuer. Used to validate tokens and (if discovery is enabled) to
+          # discover the provider's endpoints.
+          #
+          # Required if 'enabled' is true.
+          #
+          #issuer: "https://accounts.example.com/"
+
+          # oauth2 client id to use.
+          #
+          # Required if 'enabled' is true.
+          #
+          #client_id: "provided-by-your-issuer"
+
+          # oauth2 client secret to use.
+          #
+          # Required if 'enabled' is true.
+          #
+          #client_secret: "provided-by-your-issuer"
+
+          # auth method to use when exchanging the token.
+          # Valid values are 'client_secret_basic' (default), 'client_secret_post' and
+          # 'none'.
+          #
+          #client_auth_method: client_secret_post
+
+          # list of scopes to request. This should normally include the "openid" scope.
+          # Defaults to ["openid"].
+          #
+          #scopes: ["openid", "profile"]
+
+          # the oauth2 authorization endpoint. Required if provider discovery is disabled.
+          #
+          #authorization_endpoint: "https://accounts.example.com/oauth2/auth"
+
+          # the oauth2 token endpoint. Required if provider discovery is disabled.
+          #
+          #token_endpoint: "https://accounts.example.com/oauth2/token"
+
+          # the OIDC userinfo endpoint. Required if discovery is disabled and the
+          # "openid" scope is not requested.
+          #
+          #userinfo_endpoint: "https://accounts.example.com/userinfo"
+
+          # URI where to fetch the JWKS. Required if discovery is disabled and the
+          # "openid" scope is used.
+          #
+          #jwks_uri: "https://accounts.example.com/.well-known/jwks.json"
+
+          # Uncomment to skip metadata verification. Defaults to false.
+          #
+          # Use this if you are connecting to a provider that is not OpenID Connect
+          # compliant.
+          # Avoid this in production.
+          #
+          #skip_verification: true
+
+          # An external module can be provided here as a custom solution to mapping
+          # attributes returned from a OIDC provider onto a matrix user.
+          #
+          user_mapping_provider:
+            # The custom module's class. Uncomment to use a custom module.
+            # Default is {mapping_provider!r}.
             #
-            #authorization_endpoint: "https://accounts.example.com/oauth2/auth"
-
-            # the oauth2 token endpoint. Required if provider discovery is disabled.
-            #
-            #token_endpoint: "https://accounts.example.com/oauth2/token"
-
-            # the OIDC userinfo endpoint. Required if discovery is disabled and the "openid" scope is not asked.
+            # See https://github.com/matrix-org/synapse/blob/master/docs/sso_mapping_providers.md#openid-mapping-providers
+            # for information on implementing a custom mapping provider.
             #
-            #userinfo_endpoint: "https://accounts.example.com/userinfo"
+            #module: mapping_provider.OidcMappingProvider
 
-            # URI where to fetch the JWKS. Required if discovery is disabled and the "openid" scope is used.
+            # Custom configuration values for the module. This section will be passed as
+            # a Python dictionary to the user mapping provider module's `parse_config`
+            # method.
             #
-            #jwks_uri: "https://accounts.example.com/.well-known/jwks.json"
-
-            # skip metadata verification. Defaults to false.
-            # Use this if you are connecting to a provider that is not OpenID Connect compliant.
-            # Avoid this in production.
+            # The examples below are intended for the default provider: they should be
+            # changed if using a custom provider.
             #
-            #skip_verification: false
-
+            config:
+              # name of the claim containing a unique identifier for the user.
+              # Defaults to `sub`, which OpenID Connect compliant providers should provide.
+              #
+              #subject_claim: "sub"
 
-            # An external module can be provided here as a custom solution to mapping
-            # attributes returned from a OIDC provider onto a matrix user.
-            #
-            user_mapping_provider:
-              # The custom module's class. Uncomment to use a custom module.
-              # Default is {mapping_provider!r}.
+              # Jinja2 template for the localpart of the MXID.
+              #
+              # When rendering, this template is given the following variables:
+              #   * user: The claims returned by the UserInfo Endpoint and/or in the ID
+              #     Token
+              #
+              # This must be configured if using the default mapping provider.
               #
-              #module: mapping_provider.OidcMappingProvider
+              localpart_template: "{{{{ user.preferred_username }}}}"
 
-              # Custom configuration values for the module. Below options are intended
-              # for the built-in provider, they should be changed if using a custom
-              # module. This section will be passed as a Python dictionary to the
-              # module's `parse_config` method.
+              # Jinja2 template for the display name to set on first login.
               #
-              # Below is the config of the default mapping provider, based on Jinja2
-              # templates. Those templates are used to render user attributes, where the
-              # userinfo object is available through the `user` variable.
+              # If unset, no displayname will be set.
               #
-              config:
-                # name of the claim containing a unique identifier for the user.
-                # Defaults to `sub`, which OpenID Connect compliant providers should provide.
-                #
-                #subject_claim: "sub"
-
-                # Jinja2 template for the localpart of the MXID
-                #
-                localpart_template: "{{{{ user.preferred_username }}}}"
-
-                # Jinja2 template for the display name to set on first login. Optional.
-                #
-                #display_name_template: "{{{{ user.given_name }}}} {{{{ user.last_name }}}}"
+              #display_name_template: "{{{{ user.given_name }}}} {{{{ user.last_name }}}}"
         """.format(
             mapping_provider=DEFAULT_USER_MAPPING_PROVIDER
         )
diff --git a/synapse/config/saml2_config.py b/synapse/config/saml2_config.py
index 38ec256984..d0a19751e8 100644
--- a/synapse/config/saml2_config.py
+++ b/synapse/config/saml2_config.py
@@ -218,6 +218,8 @@ class SAML2Config(Config):
 
     def generate_config_section(self, config_dir_path, server_name, **kwargs):
         return """\
+        ## Single sign-on integration ##
+
         # Enable SAML2 for registration and login. Uses pysaml2.
         #
         # At least one of `sp_config` or `config_path` must be set in this section to
diff --git a/synapse/config/sso.py b/synapse/config/sso.py
index aff642f015..73b7296399 100644
--- a/synapse/config/sso.py
+++ b/synapse/config/sso.py
@@ -61,7 +61,8 @@ class SSOConfig(Config):
 
     def generate_config_section(self, **kwargs):
         return """\
-        # Additional settings to use with single-sign on systems such as SAML2 and CAS.
+        # Additional settings to use with single-sign on systems such as OpenID Connect,
+        # SAML2 and CAS.
         #
         sso:
             # A list of client URLs which are whitelisted so that the user does not
diff --git a/synapse/handlers/oidc_handler.py b/synapse/handlers/oidc_handler.py
index 4ba8c7fda5..9c08eb5399 100644
--- a/synapse/handlers/oidc_handler.py
+++ b/synapse/handlers/oidc_handler.py
@@ -37,6 +37,7 @@ from twisted.web.client import readBody
 from synapse.config import ConfigError
 from synapse.http.server import finish_request
 from synapse.http.site import SynapseRequest
+from synapse.logging.context import make_deferred_yieldable
 from synapse.push.mailer import load_jinja2_templates
 from synapse.server import HomeServer
 from synapse.types import UserID, map_username_to_mxid_localpart
@@ -99,7 +100,6 @@ class OidcHandler:
             hs.config.oidc_client_auth_method,
         )  # type: ClientAuth
         self._client_auth_method = hs.config.oidc_client_auth_method  # type: str
-        self._subject_claim = hs.config.oidc_subject_claim
         self._provider_metadata = OpenIDProviderMetadata(
             issuer=hs.config.oidc_issuer,
             authorization_endpoint=hs.config.oidc_authorization_endpoint,
@@ -310,6 +310,10 @@ class OidcHandler:
         received in the callback to exchange it for a token. The call uses the
         ``ClientAuth`` to authenticate with the client with its ID and secret.
 
+        See:
+           https://tools.ietf.org/html/rfc6749#section-3.2
+           https://openid.net/specs/openid-connect-core-1_0.html#TokenEndpoint
+
         Args:
             code: The authorization code we got from the callback.
 
@@ -362,7 +366,7 @@ class OidcHandler:
             code=response.code, phrase=response.phrase.decode("utf-8")
         )
 
-        resp_body = await readBody(response)
+        resp_body = await make_deferred_yieldable(readBody(response))
 
         if response.code >= 500:
             # In case of a server error, we should first try to decode the body
@@ -484,6 +488,7 @@ class OidcHandler:
                 claims_params=claims_params,
             )
         except ValueError:
+            logger.info("Reloading JWKS after decode error")
             jwk_set = await self.load_jwks(force=True)  # try reloading the jwks
             claims = jwt.decode(
                 token["id_token"],
@@ -592,6 +597,9 @@ class OidcHandler:
         # The provider might redirect with an error.
         # In that case, just display it as-is.
         if b"error" in request.args:
+            # error response from the auth server. see:
+            #  https://tools.ietf.org/html/rfc6749#section-4.1.2.1
+            #  https://openid.net/specs/openid-connect-core-1_0.html#AuthError
             error = request.args[b"error"][0].decode()
             description = request.args.get(b"error_description", [b""])[0].decode()
 
@@ -605,8 +613,11 @@ class OidcHandler:
             self._render_error(request, error, description)
             return
 
+        # otherwise, it is presumably a successful response. see:
+        #   https://tools.ietf.org/html/rfc6749#section-4.1.2
+
         # Fetch the session cookie
-        session = request.getCookie(SESSION_COOKIE_NAME)
+        session = request.getCookie(SESSION_COOKIE_NAME)  # type: Optional[bytes]
         if session is None:
             logger.info("No session cookie found")
             self._render_error(request, "missing_session", "No session cookie found")
@@ -654,7 +665,7 @@ class OidcHandler:
             self._render_error(request, "invalid_request", "Code parameter is missing")
             return
 
-        logger.info("Exchanging code")
+        logger.debug("Exchanging code")
         code = request.args[b"code"][0].decode()
         try:
             token = await self._exchange_code(code)
@@ -663,10 +674,12 @@ class OidcHandler:
             self._render_error(request, e.error, e.error_description)
             return
 
+        logger.debug("Successfully obtained OAuth2 access token")
+
         # Now that we have a token, get the userinfo, either by decoding the
         # `id_token` or by fetching the `userinfo_endpoint`.
         if self._uses_userinfo:
-            logger.info("Fetching userinfo")
+            logger.debug("Fetching userinfo")
             try:
                 userinfo = await self._fetch_userinfo(token)
             except Exception as e:
@@ -674,7 +687,7 @@ class OidcHandler:
                 self._render_error(request, "fetch_error", str(e))
                 return
         else:
-            logger.info("Extracting userinfo from id_token")
+            logger.debug("Extracting userinfo from id_token")
             try:
                 userinfo = await self._parse_id_token(token, nonce=nonce)
             except Exception as e:
@@ -750,7 +763,7 @@ class OidcHandler:
         return macaroon.serialize()
 
     def _verify_oidc_session_token(
-        self, session: str, state: str
+        self, session: bytes, state: str
     ) -> Tuple[str, str, Optional[str]]:
         """Verifies and extract an OIDC session token.
 
-- 
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