Record mappings from saml users in an external table

We want to assign unique mxids to saml users based on an incrementing
suffix. For that to work, we need to record the allocated mxid in a separate
table.

docs/sample_config.yaml

@@ -1099,6 +1099,32 @@ saml2_config:
   #
   #saml_session_lifetime: 5m
 
+  # The SAML attribute (after mapping via the attribute maps) to use to derive
+  # the Matrix ID from. 'uid' by default.
+  #
+  #mxid_source_attribute: displayName
+
+  # The mapping system to use for mapping the saml attribute onto a matrix ID.
+  # Options include:
+  #  * 'hexencode' (which maps unpermitted characters to '=xx')
+  #  * 'dotreplace' (which replaces unpermitted characters with '.').
+  # The default is 'hexencode'.
+  #
+  #mxid_mapping: dotreplace
+
+  # In previous versions of synapse, the mapping from SAML attribute to MXID was
+  # always calculated dynamically rather than stored in a table. For backwards-
+  # compatibility, we will look for user_ids matching such a pattern before
+  # creating a new account.
+  #
+  # This setting controls the SAML attribute which will be used for this
+  # backwards-compatibility lookup. Typically it should be 'uid', but if the
+  # attribute maps are changed, it may be necessary to change it.
+  #
+  # The default is 'uid'.
+  #
+  #grandfathered_mxid_source_attribute: upn
+
 
 
 # Enable CAS for registration and login.

synapse/config/saml2_config.py

@@ -12,7 +12,13 @@
 # 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 re
+
 from synapse.python_dependencies import DependencyException, check_requirements
+from synapse.types import (
+    map_username_to_mxid_localpart,
+    mxid_localpart_allowed_characters,
+)
 
 from ._base import Config, ConfigError
 
@@ -36,6 +42,14 @@ class SAML2Config(Config):
 
         self.saml2_enabled = True
 
+        self.saml2_mxid_source_attribute = saml2_config.get(
+            "mxid_source_attribute", "uid"
+        )
+
+        self.saml2_grandfathered_mxid_source_attribute = saml2_config.get(
+            "grandfathered_mxid_source_attribute", "uid"
+        )
+
         import saml2.config
 
         self.saml2_sp_config = saml2.config.SPConfig()
@@ -51,6 +65,12 @@ class SAML2Config(Config):
             saml2_config.get("saml_session_lifetime", "5m")
         )
 
+        mapping = saml2_config.get("mxid_mapping", "hexencode")
+        try:
+            self.saml2_mxid_mapper = MXID_MAPPER_MAP[mapping]
+        except KeyError:
+            raise ConfigError("%s is not a known mxid_mapping" % (mapping,))
+
     def _default_saml_config_dict(self):
         import saml2
 
@@ -58,6 +78,13 @@ class SAML2Config(Config):
         if public_baseurl is None:
             raise ConfigError("saml2_config requires a public_baseurl to be set")
 
+        required_attributes = {"uid", self.saml2_mxid_source_attribute}
+
+        optional_attributes = {"displayName"}
+        if self.saml2_grandfathered_mxid_source_attribute:
+            optional_attributes.add(self.saml2_grandfathered_mxid_source_attribute)
+        optional_attributes -= required_attributes
+
         metadata_url = public_baseurl + "_matrix/saml2/metadata.xml"
         response_url = public_baseurl + "_matrix/saml2/authn_response"
         return {
@@ -69,8 +96,9 @@ class SAML2Config(Config):
                             (response_url, saml2.BINDING_HTTP_POST)
                         ]
                     },
-                    "required_attributes": ["uid"],
+                    "required_attributes": list(required_attributes),
-                    "optional_attributes": ["mail", "surname", "givenname"],
+                    "optional_attributes": list(optional_attributes),
+                    # "name_id_format": saml2.saml.NAMEID_FORMAT_PERSISTENT,
                 }
             },
         }
@@ -146,6 +174,52 @@ class SAML2Config(Config):
           # The default is 5 minutes.
           #
           #saml_session_lifetime: 5m
+
+          # The SAML attribute (after mapping via the attribute maps) to use to derive
+          # the Matrix ID from. 'uid' by default.
+          #
+          #mxid_source_attribute: displayName
+
+          # The mapping system to use for mapping the saml attribute onto a matrix ID.
+          # Options include:
+          #  * 'hexencode' (which maps unpermitted characters to '=xx')
+          #  * 'dotreplace' (which replaces unpermitted characters with '.').
+          # The default is 'hexencode'.
+          #
+          #mxid_mapping: dotreplace
+
+          # In previous versions of synapse, the mapping from SAML attribute to MXID was
+          # always calculated dynamically rather than stored in a table. For backwards-
+          # compatibility, we will look for user_ids matching such a pattern before
+          # creating a new account.
+          #
+          # This setting controls the SAML attribute which will be used for this
+          # backwards-compatibility lookup. Typically it should be 'uid', but if the
+          # attribute maps are changed, it may be necessary to change it.
+          #
+          # The default is 'uid'.
+          #
+          #grandfathered_mxid_source_attribute: upn
         """ % {
             "config_dir_path": config_dir_path
         }
+
+
+DOT_REPLACE_PATTERN = re.compile(
+    ("[^%s]" % (re.escape("".join(mxid_localpart_allowed_characters)),))
+)
+
+
+def dot_replace_for_mxid(username: str) -> str:
+    username = username.lower()
+    username = DOT_REPLACE_PATTERN.sub(".", username)
+
+    # regular mxids aren't allowed to start with an underscore either
+    username = re.sub("^_", "", username)
+    return username
+
+
+MXID_MAPPER_MAP = {
+    "hexencode": map_username_to_mxid_localpart,
+    "dotreplace": dot_replace_for_mxid,
+}

synapse/handlers/saml_handler.py

@@ -21,6 +21,8 @@ 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
+from synapse.types import UserID, map_username_to_mxid_localpart
+from synapse.util.async_helpers import Linearizer
 
 logger = logging.getLogger(__name__)
 
@@ -29,12 +31,26 @@ class SamlHandler:
     def __init__(self, hs):
         self._saml_client = Saml2Client(hs.config.saml2_sp_config)
         self._sso_auth_handler = SSOAuthHandler(hs)
+        self._registration_handler = hs.get_registration_handler()
+
+        self._clock = hs.get_clock()
+        self._datastore = hs.get_datastore()
+        self._hostname = hs.hostname
+        self._saml2_session_lifetime = hs.config.saml2_session_lifetime
+        self._mxid_source_attribute = hs.config.saml2_mxid_source_attribute
+        self._grandfathered_mxid_source_attribute = (
+            hs.config.saml2_grandfathered_mxid_source_attribute
+        )
+        self._mxid_mapper = hs.config.saml2_mxid_mapper
+
+        # identifier for the external_ids table
+        self._auth_provider_id = "saml"
 
         # a map from saml session id to Saml2SessionData object
         self._outstanding_requests_dict = {}
 
-        self._clock = hs.get_clock()
+        # a lock on the mappings
-        self._saml2_session_lifetime = hs.config.saml2_session_lifetime
+        self._mapping_lock = Linearizer(name="saml_mapping", clock=self._clock)
 
     def handle_redirect_request(self, client_redirect_url):
         """Handle an incoming request to /login/sso/redirect
@@ -60,7 +76,7 @@ class SamlHandler:
         # this shouldn't happen!
         raise Exception("prepare_for_authenticate didn't return a Location header")
 
-    def handle_saml_response(self, request):
+    async def handle_saml_response(self, request):
         """Handle an incoming request to /_matrix/saml2/authn_response
 
         Args:
@@ -77,6 +93,10 @@ class SamlHandler:
         # the dict.
         self.expire_sessions()
 
+        user_id = await self._map_saml_response_to_user(resp_bytes)
+        self._sso_auth_handler.complete_sso_login(user_id, request, relay_state)
+
+    async def _map_saml_response_to_user(self, resp_bytes):
         try:
             saml2_auth = self._saml_client.parse_authn_request_response(
                 resp_bytes,
@@ -91,18 +111,85 @@ class SamlHandler:
             logger.warning("SAML2 response was not signed")
             raise SynapseError(400, "SAML2 response was not signed")
 
-        if "uid" not in saml2_auth.ava:
+        try:
+            remote_user_id = saml2_auth.ava["uid"][0]
+        except KeyError:
             logger.warning("SAML2 response lacks a 'uid' attestation")
             raise SynapseError(400, "uid not in SAML2 response")
 
+        try:
+            mxid_source = saml2_auth.ava[self._mxid_source_attribute][0]
+        except KeyError:
+            logger.warning(
+                "SAML2 response lacks a '%s' attestation", self._mxid_source_attribute
+            )
+            raise SynapseError(
+                400, "%s not in SAML2 response" % (self._mxid_source_attribute,)
+            )
+
         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(
+        with (await self._mapping_lock.queue(self._auth_provider_id)):
-            username, request, relay_state, user_display_name=displayName
+            # first of all, check if we already have a mapping for this user
-        )
+            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
+
+            # backwards-compatibility hack: see if there is an existing user with a
+            # suitable mapping from the uid
+            if (
+                self._grandfathered_mxid_source_attribute
+                and self._grandfathered_mxid_source_attribute in saml2_auth.ava
+            ):
+                attrval = saml2_auth.ava[self._grandfathered_mxid_source_attribute][0]
+                user_id = UserID(
+                    map_username_to_mxid_localpart(attrval), self._hostname
+                ).to_string()
+                logger.info(
+                    "Looking for existing account based on mapped %s %s",
+                    self._grandfathered_mxid_source_attribute,
+                    user_id,
+                )
+
+                users = await self._datastore.get_users_by_id_case_insensitive(user_id)
+                if users:
+                    registered_user_id = list(users.keys())[0]
+                    logger.info("Grandfathering mapping to %s", registered_user_id)
+                    await self._datastore.record_user_external_id(
+                        self._auth_provider_id, remote_user_id, registered_user_id
+                    )
+                    return registered_user_id
+
+            # figure out a new mxid for this user
+            base_mxid_localpart = self._mxid_mapper(mxid_source)
+
+            suffix = 0
+            while True:
+                localpart = base_mxid_localpart + (str(suffix) if suffix else "")
+                if not await self._datastore.get_users_by_id_case_insensitive(
+                    UserID(localpart, self._hostname).to_string()
+                ):
+                    break
+                suffix += 1
+            logger.info("Allocating mxid for new user with localpart %s", localpart)
+
+            registered_user_id = await self._registration_handler.register_user(
+                localpart=localpart, default_display_name=displayName
+            )
+            await self._datastore.record_user_external_id(
+                self._auth_provider_id, remote_user_id, registered_user_id
+            )
+            return registered_user_id
 
     def expire_sessions(self):
         expire_before = self._clock.time_msec() - self._saml2_session_lifetime

synapse/rest/client/v1/login.py

@@ -29,6 +29,7 @@ from synapse.http.servlet import (
     parse_json_object_from_request,
     parse_string,
 )
+from synapse.http.site import SynapseRequest
 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
@@ -507,6 +508,19 @@ class SSOAuthHandler(object):
                 localpart=localpart, default_display_name=user_display_name
             )
 
+        self.complete_sso_login(registered_user_id, request, client_redirect_url)
+
+    def complete_sso_login(
+        self, registered_user_id: str, request: SynapseRequest, client_redirect_url: str
+    ):
+        """Having figured out a mxid for this user, complete the HTTP request
+
+        Args:
+            registered_user_id:
+            request:
+            client_redirect_url:
+        """
+
         login_token = self._macaroon_gen.generate_short_term_login_token(
             registered_user_id
         )

synapse/storage/registration.py

@@ -22,6 +22,7 @@ from six import iterkeys
 from six.moves import range
 
 from twisted.internet import defer
+from twisted.internet.defer import Deferred
 
 from synapse.api.constants import UserTypes
 from synapse.api.errors import Codes, StoreError, ThreepidValidationError
@@ -337,6 +338,26 @@ class RegistrationWorkerStore(SQLBaseStore):
 
         return self.runInteraction("get_users_by_id_case_insensitive", f)
 
+    async def get_user_by_external_id(
+        self, auth_provider: str, external_id: str
+    ) -> str:
+        """Look up a user by their external auth id
+
+        Args:
+            auth_provider: identifier for the remote auth provider
+            external_id: id on that system
+
+        Returns:
+            str|None: the mxid of the user, or None if they are not known
+        """
+        return await self._simple_select_one_onecol(
+            table="user_external_ids",
+            keyvalues={"auth_provider": auth_provider, "external_id": external_id},
+            retcol="user_id",
+            allow_none=True,
+            desc="get_user_by_external_id",
+        )
+
     @defer.inlineCallbacks
     def count_all_users(self):
         """Counts all users registered on the homeserver."""
@@ -848,6 +869,26 @@ class RegistrationStore(
         self._invalidate_cache_and_stream(txn, self.get_user_by_id, (user_id,))
         txn.call_after(self.is_guest.invalidate, (user_id,))
 
+    def record_user_external_id(
+        self, auth_provider: str, external_id: str, user_id: str
+    ) -> Deferred:
+        """Record a mapping from an external user id to a mxid
+
+        Args:
+            auth_provider: identifier for the remote auth provider
+            external_id: id on that system
+            user_id: complete mxid that it is mapped to
+        """
+        return self._simple_insert(
+            table="user_external_ids",
+            values={
+                "auth_provider": auth_provider,
+                "external_id": external_id,
+                "user_id": user_id,
+            },
+            desc="record_user_external_id",
+        )
+
     def user_set_password_hash(self, user_id, password_hash):
         """
         NB. This does *not* evict any cache because the one use for this

synapse/storage/schema/delta/56/user_external_ids.sql

@@ -0,0 +1,24 @@
+/* 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.
+ */
+
+/*
+ * a table which records mappings from external auth providers to mxids
+ */
+CREATE TABLE IF NOT EXISTS user_external_ids (
+    auth_provider TEXT NOT NULL,
+    external_id TEXT NOT NULL,
+    user_id TEXT NOT NULL,
+    UNIQUE (auth_provider, external_id)
+);