Implement SAML2 authentication (#4267)

This implements both a SAML2 metadata endpoint (at
`/_matrix/saml2/metadata.xml`), and a SAML2 response receiver (at
`/_matrix/saml2/authn_response`). If the SAML2 response matches what's been
configured, we complete the SSO login flow by redirecting to the client url
(aka `RelayState` in SAML2 jargon) with a login token.

What we don't yet have is anything to build a SAML2 request and redirect the
user to the identity provider. That is left as an exercise for the reader.

9 files changed, 258 insertions, 2 deletions

diff --git a/changelog.d/4267.feature b/changelog.d/4267.feature
new file mode 100644
index 0000000000..da36986e2b
--- /dev/null
+++ b/changelog.d/4267.feature
@@ -0,0 +1 @@
+Rework SAML2 authentication
diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index a03a3e4b8a..1e495a38b9 100755
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -199,6 +199,10 @@ class SynapseHomeServer(HomeServer):
                 "/.well-known/matrix/client": WellKnownResource(self),
             })
 
+            if self.get_config().saml2_enabled:
+                from synapse.rest.saml2 import SAML2Resource
+                resources["/_matrix/saml2"] = SAML2Resource(self)
+
         if name == "consent":
             from synapse.rest.consent.consent_resource import ConsentResource
             consent_resource = ConsentResource(self)
diff --git a/synapse/config/homeserver.py b/synapse/config/homeserver.py
index 36182267c2..9d740c7a71 100644
--- a/synapse/config/homeserver.py
+++ b/synapse/config/homeserver.py
@@ -32,6 +32,7 @@ from .ratelimiting import RatelimitConfig
 from .registration import RegistrationConfig
 from .repository import ContentRepositoryConfig
 from .room_directory import RoomDirectoryConfig
+from .saml2_config import SAML2Config
 from .server import ServerConfig
 from .server_notices_config import ServerNoticesConfig
 from .spam_checker import SpamCheckerConfig
@@ -44,7 +45,7 @@ from .workers import WorkerConfig
 class HomeServerConfig(TlsConfig, ServerConfig, DatabaseConfig, LoggingConfig,
                        RatelimitConfig, ContentRepositoryConfig, CaptchaConfig,
                        VoipConfig, RegistrationConfig, MetricsConfig, ApiConfig,
-                       AppServiceConfig, KeyConfig, CasConfig,
+                       AppServiceConfig, KeyConfig, SAML2Config, CasConfig,
                        JWTConfig, PasswordConfig, EmailConfig,
                        WorkerConfig, PasswordAuthProviderConfig, PushConfig,
                        SpamCheckerConfig, GroupsConfig, UserDirectoryConfig,
diff --git a/synapse/config/saml2_config.py b/synapse/config/saml2_config.py
new file mode 100644
index 0000000000..86ffe334f5
--- /dev/null
+++ b/synapse/config/saml2_config.py
@@ -0,0 +1,110 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd.
+#
+# 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 ._base import Config, ConfigError
+
+
+class SAML2Config(Config):
+    def read_config(self, config):
+        self.saml2_enabled = False
+
+        saml2_config = config.get("saml2_config")
+
+        if not saml2_config or not saml2_config.get("enabled", True):
+            return
+
+        self.saml2_enabled = True
+
+        import saml2.config
+        self.saml2_sp_config = saml2.config.SPConfig()
+        self.saml2_sp_config.load(self._default_saml_config_dict())
+        self.saml2_sp_config.load(saml2_config.get("sp_config", {}))
+
+        config_path = saml2_config.get("config_path", None)
+        if config_path is not None:
+            self.saml2_sp_config.load_file(config_path)
+
+    def _default_saml_config_dict(self):
+        import saml2
+
+        public_baseurl = self.public_baseurl
+        if public_baseurl is None:
+            raise ConfigError(
+                "saml2_config requires a public_baseurl to be set"
+            )
+
+        metadata_url = public_baseurl + "_matrix/saml2/metadata.xml"
+        response_url = public_baseurl + "_matrix/saml2/authn_response"
+        return {
+            "entityid": metadata_url,
+
+            "service": {
+                "sp": {
+                    "endpoints": {
+                        "assertion_consumer_service": [
+                            (response_url, saml2.BINDING_HTTP_POST),
+                        ],
+                    },
+                    "required_attributes": ["uid"],
+                    "optional_attributes": ["mail", "surname", "givenname"],
+                },
+            }
+        }
+
+    def default_config(self, config_dir_path, server_name, **kwargs):
+        return """
+        # Enable SAML2 for registration and login. Uses pysaml2.
+        #
+        # saml2_config:
+        #
+        #   # The following is the configuration for the pysaml2 Service Provider.
+        #   # See pysaml2 docs for format of config.
+        #   #
+        #   # Default values will be used for the 'entityid' and 'service' settings,
+        #   # so it is not normally necessary to specify them unless you need to
+        #   # override them.
+        #
+        #   sp_config:
+        #     # point this to the IdP's metadata. You can use either a local file or
+        #     # (preferably) a URL.
+        #     metadata:
+        #       # local: ["saml2/idp.xml"]
+        #       remote:
+        #         - url: https://our_idp/metadata.xml
+        #
+        #     # The following is 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!
+        #
+        #     description: ["My awesome SP", "en"]
+        #     name: ["Test SP", "en"]
+        #
+        #     organization:
+        #       name: Example com
+        #       display_name:
+        #         - ["Example co", "en"]
+        #       url: "http://example.com"
+        #
+        #     contact_person:
+        #       - given_name: Bob
+        #         sur_name: "the Sysadmin"
+        #         email_address": ["admin@example.com"]
+        #         contact_type": technical
+        #
+        #   # Instead of putting the config inline as above, you can specify a
+        #   # separate pysaml2 configuration file:
+        #   #
+        #   # config_path: "%(config_dir_path)s/sp_conf.py"
+        """ % {"config_dir_path": config_dir_path}
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 75ba9947cc..db631e0c6c 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -80,7 +80,10 @@ CONDITIONAL_REQUIREMENTS = {
     },
     "postgres": {
         "psycopg2>=2.6": ["psycopg2"]
-    }
+    },
+    "saml2": {
+        "pysaml2>=4.5.0": ["saml2"],
+    },
 }
 
 
diff --git a/synapse/rest/saml2/__init__.py b/synapse/rest/saml2/__init__.py
new file mode 100644
index 0000000000..68da37ca6a
--- /dev/null
+++ b/synapse/rest/saml2/__init__.py
@@ -0,0 +1,29 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# 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.saml2.metadata_resource import SAML2MetadataResource
+from synapse.rest.saml2.response_resource import SAML2ResponseResource
+
+logger = logging.getLogger(__name__)
+
+
+class SAML2Resource(Resource):
+    def __init__(self, hs):
+        Resource.__init__(self)
+        self.putChild(b"metadata.xml", SAML2MetadataResource(hs))
+        self.putChild(b"authn_response", SAML2ResponseResource(hs))
diff --git a/synapse/rest/saml2/metadata_resource.py b/synapse/rest/saml2/metadata_resource.py
new file mode 100644
index 0000000000..e8c680aeb4
--- /dev/null
+++ b/synapse/rest/saml2/metadata_resource.py
@@ -0,0 +1,36 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# 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 saml2.metadata
+
+from twisted.web.resource import Resource
+
+
+class SAML2MetadataResource(Resource):
+    """A Twisted web resource which renders the SAML metadata"""
+
+    isLeaf = 1
+
+    def __init__(self, hs):
+        Resource.__init__(self)
+        self.sp_config = hs.config.saml2_sp_config
+
+    def render_GET(self, request):
+        metadata_xml = saml2.metadata.create_metadata_string(
+            configfile=None, config=self.sp_config,
+        )
+        request.setHeader(b"Content-Type", b"text/xml; charset=utf-8")
+        return metadata_xml
diff --git a/synapse/rest/saml2/response_resource.py b/synapse/rest/saml2/response_resource.py
new file mode 100644
index 0000000000..ad2ed157b5
--- /dev/null
+++ b/synapse/rest/saml2/response_resource.py
@@ -0,0 +1,71 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright 2018 New Vector Ltd
+#
+# 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 saml2
+from saml2.client import Saml2Client
+
+from twisted.web.resource import Resource
+from twisted.web.server import NOT_DONE_YET
+
+from synapse.api.errors import CodeMessageException
+from synapse.http.server import 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(Resource):
+    """A Twisted web resource which handles the SAML response"""
+
+    isLeaf = 1
+
+    def __init__(self, hs):
+        Resource.__init__(self)
+
+        self._saml_client = Saml2Client(hs.config.saml2_sp_config)
+        self._sso_auth_handler = SSOAuthHandler(hs)
+
+    def render_POST(self, request):
+        self._async_render_POST(request)
+        return NOT_DONE_YET
+
+    @wrap_html_request_handler
+    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]
+        return self._sso_auth_handler.on_successful_auth(
+            username, request, relay_state,
+        )
diff --git a/tests/utils.py b/tests/utils.py
index 52ab762010..04796a9b30 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -139,6 +139,7 @@ def default_config(name):
     config.admin_contact = None
     config.rc_messages_per_second = 10000
     config.rc_message_burst_count = 10000
+    config.saml2_enabled = False
 
     config.use_frozen_dicts = False