Disable validation that a UI authentication session has not been modi…

…fied during a request cycle.

Partial backout of 1c1242a (#7068)

synapse/handlers/auth.py

@@ -329,18 +329,6 @@ async def check_auth(
                 # isn't arbitrary.
                 clientdict = session.clientdict
 
-            # Ensure that the queried operation does not vary between stages of
-            # the UI authentication session. This is done by generating a stable
-            # comparator based on the URI, method, and body (minus the auth dict)
-            # and storing it during the initial query. Subsequent queries ensure
-            # that this comparator has not changed.
-            comparator = (uri, method, clientdict)
-            if (session.uri, session.method, session.clientdict) != comparator:
-                raise SynapseError(
-                    403,
-                    "Requested operation has changed during the UI authentication session.",
-                )
-
         if not authdict:
             raise InteractiveAuthIncompleteError(
                 self._auth_dict_for_flows(flows, session.session_id)