Complete the SAML2 implementation (#5422)

* SAML2 Improvements and redirect stuff

Signed-off-by: Alexander Trost <galexrt@googlemail.com>

* Code cleanups and simplifications.

Also: share the saml client between redirect and response handlers.

* changelog

* Revert redundant changes to static js

* Move all the saml stuff out to a centralised handler

* Add support for tracking SAML2 sessions.

This allows us to correctly handle `allow_unsolicited: False`.

* update sample config

* cleanups

* update sample config

* rename BaseSSORedirectServlet for consistency

* Address review comments

7 files changed, 231 insertions, 45 deletions

diff --git a/changelog.d/5422.feature b/changelog.d/5422.feature
new file mode 100644
index 0000000000..02ac25a2f4
--- /dev/null
+++ b/changelog.d/5422.feature
@@ -0,0 +1 @@
+Fully support SAML2 authentication. Contributed by [Alexander Trost](https://github.com/galexrt) - thank you!
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index bf9cd88b15..7fe7c94ac4 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -997,6 +997,12 @@ signing_key_path: "CONFDIR/SERVERNAME.signing.key"
 # so it is not normally necessary to specify them unless you need to
 # override them.
 #
+# Once SAML support is enabled, a metadata file will be exposed at
+# https://<server>:<port>/_matrix/saml2/metadata.xml, which you may be able to
+# use to configure your SAML IdP with. Alternatively, you can manually configure
+# the IdP to use an ACS location of
+# https://<server>:<port>/_matrix/saml2/authn_response.
+#
 #saml2_config:
 #  sp_config:
 #    # point this to the IdP's metadata. You can use either a local file or
@@ -1006,7 +1012,15 @@ signing_key_path: "CONFDIR/SERVERNAME.signing.key"
 #      remote:
 #        - url: https://our_idp/metadata.xml
 #
-#    # The rest of sp_config is just used to generate our metadata xml, and you
+#    # By default, the user has to go to our login page first. If you'd like to
+#    # allow IdP-initiated login, set 'allow_unsolicited: True' in a
+#    # 'service.sp' section:
+#    #
+#    #service:
+#    #  sp:
+#    #    allow_unsolicited: True
+#
+#    # The examples below are just used to generate our metadata xml, and you
 #    # may well not need it, depending on your setup. Alternatively you
 #    # may need a whole lot more detail - see the pysaml2 docs!
 #
@@ -1029,6 +1043,12 @@ signing_key_path: "CONFDIR/SERVERNAME.signing.key"
 #  # separate pysaml2 configuration file:
 #  #
 #  config_path: "CONFDIR/sp_conf.py"
+#
+#  # the lifetime of a SAML session. This defines how long a user has to
+#  # complete the authentication process, if allow_unsolicited is unset.
+#  # The default is 5 minutes.
+#  #
+#  # saml_session_lifetime: 5m
 
 
 
diff --git a/synapse/config/saml2_config.py b/synapse/config/saml2_config.py
index 872a1ba934..6a8161547a 100644
--- a/synapse/config/saml2_config.py
+++ b/synapse/config/saml2_config.py
@@ -12,6 +12,7 @@
 # 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 ._base import Config, ConfigError
 
@@ -25,6 +26,11 @@ class SAML2Config(Config):
         if not saml2_config or not saml2_config.get("enabled", True):
             return
 
+        try:
+            check_requirements("saml2")
+        except DependencyException as e:
+            raise ConfigError(e.message)
+
         self.saml2_enabled = True
 
         import saml2.config
@@ -37,6 +43,11 @@ class SAML2Config(Config):
         if config_path is not None:
             self.saml2_sp_config.load_file(config_path)
 
+        # session lifetime: in milliseconds
+        self.saml2_session_lifetime = self.parse_duration(
+            saml2_config.get("saml_session_lifetime", "5m")
+        )
+
     def _default_saml_config_dict(self):
         import saml2
 
@@ -72,6 +83,12 @@ class SAML2Config(Config):
         # so it is not normally necessary to specify them unless you need to
         # override them.
         #
+        # Once SAML support is enabled, a metadata file will be exposed at
+        # https://<server>:<port>/_matrix/saml2/metadata.xml, which you may be able to
+        # use to configure your SAML IdP with. Alternatively, you can manually configure
+        # the IdP to use an ACS location of
+        # https://<server>:<port>/_matrix/saml2/authn_response.
+        #
         #saml2_config:
         #  sp_config:
         #    # point this to the IdP's metadata. You can use either a local file or
@@ -81,7 +98,15 @@ class SAML2Config(Config):
         #      remote:
         #        - url: https://our_idp/metadata.xml
         #
-        #    # The rest of sp_config is just used to generate our metadata xml, and you
+        #    # By default, the user has to go to our login page first. If you'd like to
+        #    # allow IdP-initiated login, set 'allow_unsolicited: True' in a
+        #    # 'service.sp' section:
+        #    #
+        #    #service:
+        #    #  sp:
+        #    #    allow_unsolicited: True
+        #
+        #    # The examples below are just used to generate our metadata xml, and you
         #    # may well not need it, depending on your setup. Alternatively you
         #    # may need a whole lot more detail - see the pysaml2 docs!
         #
@@ -104,6 +129,12 @@ class SAML2Config(Config):
         #  # separate pysaml2 configuration file:
         #  #
         #  config_path: "%(config_dir_path)s/sp_conf.py"
+        #
+        #  # the lifetime of a SAML session. This defines how long a user has to
+        #  # complete the authentication process, if allow_unsolicited is unset.
+        #  # The default is 5 minutes.
+        #  #
+        #  # saml_session_lifetime: 5m
         """ % {
             "config_dir_path": config_dir_path
         }
diff --git a/synapse/handlers/saml_handler.py b/synapse/handlers/saml_handler.py
new file mode 100644
index 0000000000..a1ce6929cf
--- /dev/null
+++ b/synapse/handlers/saml_handler.py
@@ -0,0 +1,123 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 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.
+import logging
+
+import attr
+import saml2
+from saml2.client import Saml2Client
+
+from synapse.api.errors import SynapseError
+from synapse.http.servlet import parse_string
+from synapse.rest.client.v1.login import SSOAuthHandler
+
+logger = logging.getLogger(__name__)
+
+
+class SamlHandler:
+    def __init__(self, hs):
+        self._saml_client = Saml2Client(hs.config.saml2_sp_config)
+        self._sso_auth_handler = SSOAuthHandler(hs)
+
+        # a map from saml session id to Saml2SessionData object
+        self._outstanding_requests_dict = {}
+
+        self._clock = hs.get_clock()
+        self._saml2_session_lifetime = hs.config.saml2_session_lifetime
+
+    def handle_redirect_request(self, client_redirect_url):
+        """Handle an incoming request to /login/sso/redirect
+
+        Args:
+            client_redirect_url (bytes): the URL that we should redirect the
+                client to when everything is done
+
+        Returns:
+            bytes: URL to redirect to
+        """
+        reqid, info = self._saml_client.prepare_for_authenticate(
+            relay_state=client_redirect_url
+        )
+
+        now = self._clock.time_msec()
+        self._outstanding_requests_dict[reqid] = Saml2SessionData(creation_time=now)
+
+        for key, value in info["headers"]:
+            if key == "Location":
+                return value
+
+        # this shouldn't happen!
+        raise Exception("prepare_for_authenticate didn't return a Location header")
+
+    def handle_saml_response(self, request):
+        """Handle an incoming request to /_matrix/saml2/authn_response
+
+        Args:
+            request (SynapseRequest): the incoming request from the browser. We'll
+                respond to it with a redirect.
+
+        Returns:
+            Deferred[none]: Completes once we have handled the request.
+        """
+        resp_bytes = parse_string(request, "SAMLResponse", required=True)
+        relay_state = parse_string(request, "RelayState", required=True)
+
+        # expire outstanding sessions before parse_authn_request_response checks
+        # the dict.
+        self.expire_sessions()
+
+        try:
+            saml2_auth = self._saml_client.parse_authn_request_response(
+                resp_bytes,
+                saml2.BINDING_HTTP_POST,
+                outstanding=self._outstanding_requests_dict,
+            )
+        except Exception as e:
+            logger.warning("Exception parsing SAML2 response: %s", e)
+            raise SynapseError(400, "Unable to parse SAML2 response: %s" % (e,))
+
+        if saml2_auth.not_signed:
+            logger.warning("SAML2 response was not signed")
+            raise SynapseError(400, "SAML2 response was not signed")
+
+        if "uid" not in saml2_auth.ava:
+            logger.warning("SAML2 response lacks a 'uid' attestation")
+            raise SynapseError(400, "uid not in SAML2 response")
+
+        self._outstanding_requests_dict.pop(saml2_auth.in_response_to, None)
+
+        username = saml2_auth.ava["uid"][0]
+        displayName = saml2_auth.ava.get("displayName", [None])[0]
+
+        return self._sso_auth_handler.on_successful_auth(
+            username, request, relay_state, user_display_name=displayName
+        )
+
+    def expire_sessions(self):
+        expire_before = self._clock.time_msec() - self._saml2_session_lifetime
+        to_expire = set()
+        for reqid, data in self._outstanding_requests_dict.items():
+            if data.creation_time < expire_before:
+                to_expire.add(reqid)
+        for reqid in to_expire:
+            logger.debug("Expiring session id %s", reqid)
+            del self._outstanding_requests_dict[reqid]
+
+
+@attr.s
+class Saml2SessionData:
+    """Data we track about SAML2 sessions"""
+
+    # time the session was created, in milliseconds
+    creation_time = attr.ib()
diff --git a/synapse/rest/client/v1/login.py b/synapse/rest/client/v1/login.py
index e88d2ad7bd..f961178235 100644
--- a/synapse/rest/client/v1/login.py
+++ b/synapse/rest/client/v1/login.py
@@ -86,6 +86,7 @@ class LoginRestServlet(RestServlet):
         self.jwt_enabled = hs.config.jwt_enabled
         self.jwt_secret = hs.config.jwt_secret
         self.jwt_algorithm = hs.config.jwt_algorithm
+        self.saml2_enabled = hs.config.saml2_enabled
         self.cas_enabled = hs.config.cas_enabled
         self.auth_handler = self.hs.get_auth_handler()
         self.registration_handler = hs.get_registration_handler()
@@ -97,6 +98,9 @@ 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})
 
@@ -351,27 +355,49 @@ class LoginRestServlet(RestServlet):
         defer.returnValue(result)
 
 
-class CasRedirectServlet(RestServlet):
+class BaseSSORedirectServlet(RestServlet):
+    """Common base class for /login/sso/redirect impls"""
+
     PATTERNS = client_patterns("/login/(cas|sso)/redirect", v1=True)
 
+    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]
+        sso_url = self.get_sso_url(client_redirect_url)
+        request.redirect(sso_url)
+        finish_request(request)
+
+    def get_sso_url(self, client_redirect_url):
+        """Get the URL to redirect to, to perform SSO auth
+
+        Args:
+            client_redirect_url (bytes): the URL that we should redirect the
+                client to when everything is done
+
+        Returns:
+            bytes: URL to redirect to
+        """
+        # to be implemented by subclasses
+        raise NotImplementedError()
+
+
+class CasRedirectServlet(BaseSSORedirectServlet):
     def __init__(self, hs):
         super(CasRedirectServlet, self).__init__()
         self.cas_server_url = hs.config.cas_server_url.encode("ascii")
         self.cas_service_url = hs.config.cas_service_url.encode("ascii")
 
-    def on_GET(self, request):
-        args = request.args
-        if b"redirectUrl" not in args:
-            return (400, "Redirect URL not specified for CAS auth")
+    def get_sso_url(self, client_redirect_url):
         client_redirect_url_param = urllib.parse.urlencode(
-            {b"redirectUrl": args[b"redirectUrl"][0]}
+            {b"redirectUrl": client_redirect_url}
         ).encode("ascii")
         hs_redirect_url = self.cas_service_url + b"/_matrix/client/r0/login/cas/ticket"
         service_param = urllib.parse.urlencode(
             {b"service": b"%s?%s" % (hs_redirect_url, client_redirect_url_param)}
         ).encode("ascii")
-        request.redirect(b"%s/login?%s" % (self.cas_server_url, service_param))
-        finish_request(request)
+        return b"%s/login?%s" % (self.cas_server_url, service_param)
 
 
 class CasTicketServlet(RestServlet):
@@ -454,6 +480,16 @@ class CasTicketServlet(RestServlet):
         return user, attributes
 
 
+class SAMLRedirectServlet(BaseSSORedirectServlet):
+    PATTERNS = client_patterns("/login/sso/redirect", v1=True)
+
+    def __init__(self, hs):
+        self._saml_handler = hs.get_saml_handler()
+
+    def get_sso_url(self, client_redirect_url):
+        return self._saml_handler.handle_redirect_request(client_redirect_url)
+
+
 class SSOAuthHandler(object):
     """
     Utility class for Resources and Servlets which handle the response from a SSO
@@ -529,3 +565,5 @@ def register_servlets(hs, http_server):
     if hs.config.cas_enabled:
         CasRedirectServlet(hs).register(http_server)
         CasTicketServlet(hs).register(http_server)
+    elif hs.config.saml2_enabled:
+        SAMLRedirectServlet(hs).register(http_server)
diff --git a/synapse/rest/saml2/response_resource.py b/synapse/rest/saml2/response_resource.py
index 939c87306c..69ecc5e4b4 100644
--- a/synapse/rest/saml2/response_resource.py
+++ b/synapse/rest/saml2/response_resource.py
@@ -13,17 +13,8 @@
 # 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
 
-import saml2
-from saml2.client import Saml2Client
-
-from synapse.api.errors import CodeMessageException
 from synapse.http.server import DirectServeResource, wrap_html_request_handler
-from synapse.http.servlet import parse_string
-from synapse.rest.client.v1.login import SSOAuthHandler
-
-logger = logging.getLogger(__name__)
 
 
 class SAML2ResponseResource(DirectServeResource):
@@ -33,32 +24,8 @@ class SAML2ResponseResource(DirectServeResource):
 
     def __init__(self, hs):
         super().__init__()
-
-        self._saml_client = Saml2Client(hs.config.saml2_sp_config)
-        self._sso_auth_handler = SSOAuthHandler(hs)
+        self._saml_handler = hs.get_saml_handler()
 
     @wrap_html_request_handler
     async def _async_render_POST(self, request):
-        resp_bytes = parse_string(request, "SAMLResponse", required=True)
-        relay_state = parse_string(request, "RelayState", required=True)
-
-        try:
-            saml2_auth = self._saml_client.parse_authn_request_response(
-                resp_bytes, saml2.BINDING_HTTP_POST
-            )
-        except Exception as e:
-            logger.warning("Exception parsing SAML2 response", exc_info=1)
-            raise CodeMessageException(400, "Unable to parse SAML2 response: %s" % (e,))
-
-        if saml2_auth.not_signed:
-            raise CodeMessageException(400, "SAML2 response was not signed")
-
-        if "uid" not in saml2_auth.ava:
-            raise CodeMessageException(400, "uid not in SAML2 response")
-
-        username = saml2_auth.ava["uid"][0]
-
-        displayName = saml2_auth.ava.get("displayName", [None])[0]
-        return self._sso_auth_handler.on_successful_auth(
-            username, request, relay_state, user_display_name=displayName
-        )
+        return await self._saml_handler.handle_saml_response(request)
diff --git a/synapse/server.py b/synapse/server.py
index a9592c396c..9e28dba2b1 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -194,6 +194,7 @@ class HomeServer(object):
         "sendmail",
         "registration_handler",
         "account_validity_handler",
+        "saml_handler",
         "event_client_serializer",
     ]
 
@@ -524,6 +525,11 @@ class HomeServer(object):
     def build_account_validity_handler(self):
         return AccountValidityHandler(self)
 
+    def build_saml_handler(self):
+        from synapse.handlers.saml_handler import SamlHandler
+
+        return SamlHandler(self)
+
     def build_event_client_serializer(self):
         return EventClientSerializer(self)