Make room creations denied by user_may_create_room cause an M_FORBIDDEN error to be returned, not M_UNKNOWN

changelog.d/11672.feature

@@ -0,0 +1,4 @@
+Whenever the `spamcheck` forbids a user to create a room, a `SynapseError` with `errcode` `M_UNKNOWN` is returned to the client. However, it would be more specific to return the `errcode` `M_UNKNOWN`.
+
+Therefore, this PR will raise `M_FORBIDDEN` instead of `M_UNKNOWN` whenever `synapse/events/spamcheck.py:user_may_create_room` returns `False`.
+Note: The `M_FORBIDDEN` code is set in the methods which currently call `user_may_create_room`, not in the method `user_may_create_room` itself.

synapse/handlers/room.py

@@ -393,7 +393,9 @@ async def clone_existing_room(
  user_id = requester.user.to_string()
 
  if not await self.spam_checker.user_may_create_room(user_id):
- raise SynapseError(403, "You are not permitted to create rooms")
+ raise SynapseError(
+ 403, "You are not permitted to create rooms", Codes.FORBIDDEN
+ )
 
  creation_content: JsonDict = {
  "room_version": new_room_version.identifier,
@@ -685,7 +687,9 @@ async def create_room(
  invite_3pid_list,
  )
  ):
- raise SynapseError(403, "You are not permitted to create rooms")
+ raise SynapseError(
+ 403, "You are not permitted to create rooms", Codes.FORBIDDEN
+ )
 
  if ratelimit:
  await self.request_ratelimiter.ratelimit(requester)