Send unstable-prefixed room_type in store-invite IS API requests (#10435)

The room type is per MSC3288 to allow the identity-server to
change invitation wording based on whether the invitation is to
a room or a space.

The prefixed key will be replaced once MSC3288 is accepted
into the spec.

changelog.d/10435.feature

+Experimental support for [MSC3288](https://github.com/matrix-org/matrix-doc/pull/3288), sending `room_type` to the identity server for 3pid invites over the `/store-invite` API.

synapse/handlers/identity.py

@@ -824,6 +824,7 @@ class IdentityHandler(BaseHandler):
         room_avatar_url: str,
         room_join_rules: str,
         room_name: str,
+        room_type: Optional[str],
         inviter_display_name: str,
         inviter_avatar_url: str,
         id_access_token: Optional[str] = None,
@@ -843,6 +844,7 @@ class IdentityHandler(BaseHandler):
                 notifications.
             room_join_rules: The join rules of the email (e.g. "public").
             room_name: The m.room.name of the room.
+            room_type: The type of the room from its m.room.create event (e.g "m.space").
             inviter_display_name: The current display name of the
                 inviter.
             inviter_avatar_url: The URL of the inviter's avatar.
@@ -869,6 +871,10 @@ class IdentityHandler(BaseHandler):
             "sender_display_name": inviter_display_name,
             "sender_avatar_url": inviter_avatar_url,
         }
+
+        if room_type is not None:
+            invite_config["org.matrix.msc3288.room_type"] = room_type
+
         # If a custom web client location is available, include it in the request.
         if self._web_client_location:
             invite_config["org.matrix.web_client_location"] = self._web_client_location

synapse/handlers/room_member.py

@@ -19,7 +19,12 @@ from http import HTTPStatus
 from typing import TYPE_CHECKING, Iterable, List, Optional, Set, Tuple
 
 from synapse import types
-from synapse.api.constants import AccountDataTypes, EventTypes, Membership
+from synapse.api.constants import (
+    AccountDataTypes,
+    EventContentFields,
+    EventTypes,
+    Membership,
+)
 from synapse.api.errors import (
     AuthError,
     Codes,
@@ -1237,6 +1242,11 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
         if room_name_event:
             room_name = room_name_event.content.get("name", "")
 
+        room_type = None
+        room_create_event = room_state.get((EventTypes.Create, ""))
+        if room_create_event:
+            room_type = room_create_event.content.get(EventContentFields.ROOM_TYPE)
+
         room_join_rules = ""
         join_rules_event = room_state.get((EventTypes.JoinRules, ""))
         if join_rules_event:
@@ -1263,6 +1273,7 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
             room_avatar_url=room_avatar_url,
             room_join_rules=room_join_rules,
             room_name=room_name,
+            room_type=room_type,
             inviter_display_name=inviter_display_name,
             inviter_avatar_url=inviter_avatar_url,
             id_access_token=id_access_token,