Server notices: add an autojoin setting for the notices room (#16699)

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

changelog.d/16699.feature

@@ -0,0 +1 @@
+Add an autojoin setting for the notices room so users get joined directly instead of receiving an invite.

docs/server_notices.md

@@ -46,6 +46,7 @@ server_notices:
    system_mxid_display_name: "Server Notices"
    system_mxid_avatar_url: "mxc://server.com/oumMVlgDnLYFaPVkExemNVVZ"
    room_name: "Server Notices"
+   auto_join: true
 ```
 
 The only compulsory setting is `system_mxid_localpart`, which defines the user
@@ -55,6 +56,8 @@ room which will be created.
 `system_mxid_display_name` and `system_mxid_avatar_url` can be used to set the
 displayname and avatar of the Server Notices user.
 
+`auto_join` will autojoin users to the notices room instead of sending an invite.
+
 ## Sending notices
 
 To send server notices to users you can use the

docs/usage/configuration/config_documentation.md

@@ -3815,6 +3815,8 @@ Sub-options for this setting include:
 * `system_mxid_display_name`: set the display name of the "notices" user
 * `system_mxid_avatar_url`: set the avatar for the "notices" user
 * `room_name`: set the room name of the server notices room
+* `auto_join`: boolean. If true, the user will be automatically joined to the room instead of being invited.
+  Defaults to false. _Added in Synapse 1.98.0._
 
 Example configuration:
 ```yaml
@@ -3823,6 +3825,7 @@ server_notices:
   system_mxid_display_name: "Server Notices"
   system_mxid_avatar_url: "mxc://server.com/oumMVlgDnLYFaPVkExemNVVZ"
   room_name: "Server Notices"
+  auto_join: true
 ```
 ---
 ### `enable_room_list_search`

synapse/config/server_notices.py

@@ -48,6 +48,7 @@ class ServerNoticesConfig(Config):
         self.server_notices_mxid_display_name: Optional[str] = None
         self.server_notices_mxid_avatar_url: Optional[str] = None
         self.server_notices_room_name: Optional[str] = None
+        self.server_notices_auto_join: bool = False
 
     def read_config(self, config: JsonDict, **kwargs: Any) -> None:
         c = config.get("server_notices")
@@ -62,3 +63,4 @@ class ServerNoticesConfig(Config):
         self.server_notices_mxid_avatar_url = c.get("system_mxid_avatar_url", None)
         # todo: i18n
         self.server_notices_room_name = c.get("room_name", "Server Notices")
+        self.server_notices_auto_join = c.get("auto_join", False)

synapse/server_notices/server_notices_manager.py

@@ -224,14 +224,27 @@ class ServerNoticesManager:
             if room.room_id == room_id:
                 return
 
+        user_id_obj = UserID.from_string(user_id)
         await self._room_member_handler.update_membership(
             requester=requester,
-            target=UserID.from_string(user_id),
+            target=user_id_obj,
             room_id=room_id,
             action="invite",
             ratelimit=False,
         )
 
+        if self._config.servernotices.server_notices_auto_join:
+            user_requester = create_requester(
+                user_id, authenticated_entity=self._server_name
+            )
+            await self._room_member_handler.update_membership(
+                requester=user_requester,
+                target=user_id_obj,
+                room_id=room_id,
+                action="join",
+                ratelimit=False,
+            )
+
     async def _update_notice_user_profile_if_changed(
         self,
         requester: Requester,

tests/rest/admin/test_server_notice.py

@@ -477,6 +477,33 @@ class ServerNoticeTestCase(unittest.HomeserverTestCase):
         # second room has new ID
         self.assertNotEqual(first_room_id, second_room_id)
 
+    @override_config(
+        {"server_notices": {"system_mxid_localpart": "notices", "auto_join": True}}
+    )
+    def test_auto_join(self) -> None:
+        """
+        Tests that the user get automatically joined to the notice room
+        when `auto_join` setting is used.
+        """
+        # user has no room memberships
+        self._check_invite_and_join_status(self.other_user, 0, 0)
+
+        # send server notice
+        server_notice_request_content = {
+            "user_id": self.other_user,
+            "content": {"msgtype": "m.text", "body": "test msg one"},
+        }
+
+        self.make_request(
+            "POST",
+            self.url,
+            access_token=self.admin_user_tok,
+            content=server_notice_request_content,
+        )
+
+        # user has joined the room
+        self._check_invite_and_join_status(self.other_user, 0, 1)
+
     @override_config({"server_notices": {"system_mxid_localpart": "notices"}})
     def test_update_notice_user_name_when_changed(self) -> None:
         """