Add config option to auto-join new users to rooms

New users who register on the server will be dumped into all rooms in
auto_join_rooms in the config.

synapse/config/registration.py

@@ -41,6 +41,8 @@ class RegistrationConfig(Config):
             self.allow_guest_access and config.get("invite_3pid_guest", False)
         )
 
+        self.auto_join_rooms = config.get("auto_join_rooms", [])
+
     def default_config(self, **kwargs):
         registration_shared_secret = random_string_with_symbols(50)
 
@@ -70,6 +72,10 @@ class RegistrationConfig(Config):
             - matrix.org
             - vector.im
             - riot.im
+
+        # Users who register on this homeserver will automatically be joined to these rooms
+        #auto_join_rooms:
+        #    - "#example:example.com"
         """ % locals()
 
     def add_arguments(self, parser):

synapse/rest/client/v2_alpha/register.py

@@ -17,8 +17,10 @@
 from twisted.internet import defer
 
 import synapse
+import synapse.types
 from synapse.api.auth import get_access_token_from_request, has_access_token
 from synapse.api.constants import LoginType
+from synapse.types import RoomID, RoomAlias
 from synapse.api.errors import SynapseError, Codes, UnrecognizedRequestError
 from synapse.http.servlet import (
     RestServlet, parse_json_object_from_request, assert_params_in_request, parse_string
@@ -170,6 +172,7 @@ class RegisterRestServlet(RestServlet):
         self.auth_handler = hs.get_auth_handler()
         self.registration_handler = hs.get_handlers().registration_handler
         self.identity_handler = hs.get_handlers().identity_handler
+        self.room_member_handler = hs.get_handlers().room_member_handler
         self.device_handler = hs.get_device_handler()
         self.macaroon_gen = hs.get_macaroon_generator()
 
@@ -340,6 +343,14 @@ class RegisterRestServlet(RestServlet):
                 generate_token=False,
             )
 
+            # auto-join the user to any rooms we're supposed to dump them into
+            fake_requester = synapse.types.create_requester(registered_user_id)
+            for r in self.hs.config.auto_join_rooms:
+                try:
+                    yield self._join_user_to_room(fake_requester, r)
+                except Exception as e:
+                    logger.error("Failed to join new user to %r: %r", r, e)
+
             # remember that we've now registered that user account, and with
             #  what user ID (since the user may not have specified)
             self.auth_handler.set_session_data(
@@ -372,6 +383,29 @@ class RegisterRestServlet(RestServlet):
     def on_OPTIONS(self, _):
         return 200, {}
 
+    @defer.inlineCallbacks
+    def _join_user_to_room(self, requester, room_identifier):
+        room_id = None
+        if RoomID.is_valid(room_identifier):
+            room_id = room_identifier
+        elif RoomAlias.is_valid(room_identifier):
+            room_alias = RoomAlias.from_string(room_identifier)
+            room_id, remote_room_hosts = (
+                yield self.room_member_handler.lookup_room_alias(room_alias)
+            )
+            room_id = room_id.to_string()
+        else:
+            raise SynapseError(400, "%s was not legal room ID or room alias" % (
+                room_identifier,
+            ))
+
+        yield self.room_member_handler.update_membership(
+            requester=requester,
+            target=requester.user,
+            room_id=room_id,
+            action="join",
+        )
+
     @defer.inlineCallbacks
     def _do_appservice_registration(self, username, as_token, body):
         user_id = yield self.registration_handler.appservice_register(