Add option to allow anyone to use timestamp massaging

README.md

@@ -26,7 +26,9 @@ use the specific release tags.
 * Config option to allow specific users to send events without unnecessary
   validation.
 * Config option to allow specific users to receive events that are usually
-  filtered away (e.g. `org.matrix.dummy_event` and `m.room.aliases`)
+  filtered away (e.g. `org.matrix.dummy_event` and `m.room.aliases`).
+* Config option to allow specific users to use timestamp massaging without
+  being appservice users.
 
 ## Configuration
 Generating a new config will include the `meow` section, but this is here for
@@ -42,4 +44,7 @@ meow:
    - "@you:example.com"
    # Whether or not the admin API should be able to register invalid user IDs.
    admin_api_register_invalid: true
+   # List of users who can use timestamp massaging without being appservices
+   timestamp_override:
+   - "@you:example.com"
 ```

synapse/config/meow.py

@@ -27,6 +27,7 @@ class MeowConfig(Config):
         meow_config = config.get("meow", {})
         self.validation_override = set(meow_config.get("validation_override", []))
         self.filter_override = set(meow_config.get("filter_override", []))
+        self.timestamp_override = set(meow_config.get("timestamp_override", []))
         self.admin_api_register_invalid = meow_config.get("admin_api_register_invalid", True)
 
     def generate_config_section(self, config_dir_path, server_name, **kwargs):
@@ -40,6 +41,9 @@ class MeowConfig(Config):
         #   # List of users who will get org.matrix.dummy_event and m.room.aliases events down /sync
         #   filter_override:
         #   - "@you:example.com"
+        #   # List of users who can use timestamp massaging without being appservices
+        #   timestamp_override:
+        #   - "@you:example.com"
         #   # Whether or not the admin API should be able to register invalid user IDs.
         #   admin_api_register_invalid: true
         """

synapse/rest/client/v1/room.py

@@ -213,6 +213,7 @@ class RoomSendEventRestServlet(TransactionRestServlet):
         super().__init__(hs)
         self.event_creation_handler = hs.get_event_creation_handler()
         self.auth = hs.get_auth()
+        self.hs = hs
 
     def register(self, http_server):
         # /rooms/$roomid/send/$event_type[/$txn_id]
@@ -230,8 +231,10 @@ class RoomSendEventRestServlet(TransactionRestServlet):
             "sender": requester.user.to_string(),
         }
 
-        if b"ts" in request.args and requester.app_service:
-            event_dict["origin_server_ts"] = parse_integer(request, "ts", 0)
+        if b"ts" in request.args:
+            if (requester.app_service
+                or requester.user.to_string() in self.hs.config.meow.timestamp_override):
+                event_dict["origin_server_ts"] = parse_integer(request, "ts", 0)
 
         try:
             (