Update MSC4326 error code (#18947)

Author: tulir

changelog.d/18947.misc

@@ -0,0 +1 @@
+Update error code used when an appservice tries to masquerade as an unknown device using [MSC4326](https://github.com/matrix-org/matrix-spec-proposals/pull/4326). Contributed by @tulir @ Beeper.

synapse/api/auth/base.py

@@ -354,12 +354,10 @@ async def get_appservice_user(
                 effective_user_id, effective_device_id
             )
             if device_opt is None:
-                # For now, use 400 M_EXCLUSIVE if the device doesn't exist.
-                # This is an open thread of discussion on MSC3202 as of 2021-12-09.
                 raise AuthError(
                     400,
                     f"Application service trying to use a device that doesn't exist ('{effective_device_id}' for {effective_user_id})",
-                    Codes.EXCLUSIVE,
+                    Codes.UNKNOWN_DEVICE,
                 )
 
         return create_requester(

synapse/api/errors.py

@@ -149,6 +149,9 @@ class Codes(str, Enum):
     )
     MSC4306_NOT_IN_THREAD = "IO.ELEMENT.MSC4306.M_NOT_IN_THREAD"
 
+    # Part of MSC4326
+    UNKNOWN_DEVICE = "ORG.MATRIX.MSC4326.M_UNKNOWN_DEVICE"
+
 
 class CodeMessageException(RuntimeError):
     """An exception with integer code, a message string attributes and optional headers.

tests/api/test_auth.py

@@ -304,7 +304,7 @@ def test_get_user_by_req_appservice_valid_token_invalid_device_id(self) -> None:
 
         failure = self.get_failure(self.auth.get_user_by_req(request), AuthError)
         self.assertEqual(failure.value.code, 400)
-        self.assertEqual(failure.value.errcode, Codes.EXCLUSIVE)
+        self.assertEqual(failure.value.errcode, Codes.UNKNOWN_DEVICE)
 
     def test_get_user_by_req__puppeted_token__not_tracking_puppeted_mau(self) -> None:
         self.store.get_user_by_access_token = AsyncMock(