Add a confirmation step to the SSO login flow

5 files changed, 126 insertions, 6 deletions

diff --git a/synapse/config/_base.pyi b/synapse/config/_base.pyi
index 86bc965ee4..3053fc9d27 100644
--- a/synapse/config/_base.pyi
+++ b/synapse/config/_base.pyi
@@ -24,6 +24,7 @@ from synapse.config import (
     server,
     server_notices_config,
     spam_checker,
+    sso,
     stats,
     third_party_event_rules,
     tls,
@@ -57,6 +58,7 @@ class RootConfig:
     key: key.KeyConfig
     saml2: saml2_config.SAML2Config
     cas: cas.CasConfig
+    sso: sso.SSOConfig
     jwt: jwt_config.JWTConfig
     password: password.PasswordConfig
     email: emailconfig.EmailConfig
diff --git a/synapse/config/homeserver.py b/synapse/config/homeserver.py
index 6e348671c7..b4bca08b20 100644
--- a/synapse/config/homeserver.py
+++ b/synapse/config/homeserver.py
@@ -38,6 +38,7 @@ from .saml2_config import SAML2Config
 from .server import ServerConfig
 from .server_notices_config import ServerNoticesConfig
 from .spam_checker import SpamCheckerConfig
+from .sso import SSOConfig
 from .stats import StatsConfig
 from .third_party_event_rules import ThirdPartyRulesConfig
 from .tls import TlsConfig
@@ -65,6 +66,7 @@ class HomeServerConfig(RootConfig):
         KeyConfig,
         SAML2Config,
         CasConfig,
+        SSOConfig,
         JWTConfig,
         PasswordConfig,
         EmailConfig,
diff --git a/synapse/config/sso.py b/synapse/config/sso.py
new file mode 100644
index 0000000000..f426b65b4f
--- /dev/null
+++ b/synapse/config/sso.py
@@ -0,0 +1,74 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# 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 typing import Any, Dict
+
+import pkg_resources
+
+from ._base import Config, ConfigError
+
+
+class SSOConfig(Config):
+    """SSO Configuration
+    """
+
+    section = "sso"
+
+    def read_config(self, config, **kwargs):
+        sso_config = config.get("sso") or {}  # type: Dict[str, Any]
+
+        # Pick a template directory in order of:
+        # * The sso-specific template_dir
+        # * /path/to/synapse/install/res/templates
+        template_dir = sso_config.get("template_dir")
+        if not template_dir:
+            template_dir = pkg_resources.resource_filename("synapse", "res/templates",)
+
+        self.sso_redirect_confirm_template_dir = template_dir
+
+    def generate_config_section(self, **kwargs):
+        return """\
+        # Additional settings to use with single-sign on systems such as SAML2 and CAS.
+        #
+        sso:
+            # Directory in which Synapse will try to find the template files below.
+            # If not set, default templates from within the Synapse package will be used.
+            #
+            # DO NOT UNCOMMENT THIS SETTING unless you want to customise the templates.
+            # If you *do* uncomment it, you will need to make sure that all the templates
+            # below are in the directory.
+            #
+            # Synapse will look for the following templates in this directory:
+            #
+            # * HTML page for a confirmation step before redirecting back to the client
+            #   with the login token: 'sso_redirect_confirm.html'.
+            #
+            #   When rendering, this template is given three variables:
+            #     * redirect_url: the URL the user is about to be redirected to. Needs
+            #                     manual escaping (see
+            #                     https://jinja.palletsprojects.com/en/2.11.x/templates/#html-escaping).
+            #
+            #     * display_url: the same as `redirect_url`, but with the query
+            #                    parameters stripped. The intention is to have a
+            #                    human-readable URL to show to users, not to use it as
+            #                    the final address to redirect to. Needs manual escaping
+            #                    (see https://jinja.palletsprojects.com/en/2.11.x/templates/#html-escaping).
+            #
+            #     * server_name: the homeserver's name.
+            #
+            # You can see the default templates at:
+            # https://github.com/matrix-org/synapse/tree/master/synapse/res/templates
+            #
+            #template_dir: "res/templates"
+        """
diff --git a/synapse/res/templates/sso_redirect_confirm.html b/synapse/res/templates/sso_redirect_confirm.html
new file mode 100644
index 0000000000..20a15e1e74
--- /dev/null
+++ b/synapse/res/templates/sso_redirect_confirm.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <title>SSO redirect confirmation</title>
+</head>
+    <body>
+        <p>The application at <span style="font-weight:bold">{{ display_url | e }}</span> is requesting full access to your <span style="font-weight:bold">{{ server_name }}</span> Matrix account.</p>
+        <p>If you don't recognise this address, you should ignore this and close this tab.</p>
+        <p>
+            <a href="{{ redirect_url | e }}">I trust this address</a>
+        </p>
+    </body>
+</html>
\ No newline at end of file
diff --git a/synapse/rest/client/v1/login.py b/synapse/rest/client/v1/login.py
index 1294e080dc..1acfd01d8e 100644
--- a/synapse/rest/client/v1/login.py
+++ b/synapse/rest/client/v1/login.py
@@ -29,6 +29,7 @@ from synapse.http.servlet import (
     parse_string,
 )
 from synapse.http.site import SynapseRequest
+from synapse.push.mailer import load_jinja2_templates
 from synapse.rest.client.v2_alpha._base import client_patterns
 from synapse.rest.well_known import WellKnownBuilder
 from synapse.types import UserID, map_username_to_mxid_localpart
@@ -548,6 +549,13 @@ class SSOAuthHandler(object):
         self._registration_handler = hs.get_registration_handler()
         self._macaroon_gen = hs.get_macaroon_generator()
 
+        # Load the redirect page HTML template
+        self._template = load_jinja2_templates(
+            hs.config.sso_redirect_confirm_template_dir, ["sso_redirect_confirm.html"],
+        )[0]
+
+        self._server_name = hs.config.server_name
+
     async def on_successful_auth(
         self, username, request, client_redirect_url, user_display_name=None
     ):
@@ -592,21 +600,41 @@ class SSOAuthHandler(object):
             request:
             client_redirect_url:
         """
-
+        # Create a login token
         login_token = self._macaroon_gen.generate_short_term_login_token(
             registered_user_id
         )
-        redirect_url = self._add_login_token_to_redirect_url(
-            client_redirect_url, login_token
+
+        # Remove the query parameters from the redirect URL to get a shorter version of
+        # it. This is only to display a human-readable URL in the template, but not the
+        # URL we redirect users to.
+        redirect_url_no_params = client_redirect_url.split("?")[0]
+
+        # Append the login token to the original redirect URL (i.e. with its query
+        # parameters kept intact) to build the URL to which the template needs to
+        # redirect the users once they have clicked on the confirmation link.
+        redirect_url = self._add_query_param_to_url(
+            client_redirect_url, "loginToken", login_token
+        )
+
+        # Serve the redirect confirmation page
+        html = self._template.render(
+            display_url=redirect_url_no_params,
+            redirect_url=redirect_url,
+            server_name=self._server_name,
         )
-        request.redirect(redirect_url)
+
+        request.setResponseCode(200)
+        request.setHeader(b"Content-Type", b"text/html; charset=utf-8")
+        request.setHeader(b"Content-Length", b"%d" % (len(html),))
+        request.write(html.encode("utf8"))
         finish_request(request)
 
     @staticmethod
-    def _add_login_token_to_redirect_url(url, token):
+    def _add_query_param_to_url(url, param_name, param):
         url_parts = list(urllib.parse.urlparse(url))
         query = dict(urllib.parse.parse_qsl(url_parts[4]))
-        query.update({"loginToken": token})
+        query.update({param_name: param})
         url_parts[4] = urllib.parse.urlencode(query)
         return urllib.parse.urlunparse(url_parts)