When logging in fetch user by user_id case insensitively, *unless* there are multiple case insensitive matches, in which case require the exact user_id

synapse/storage/registration.py

@@ -99,13 +99,16 @@ class RegistrationStore(SQLBaseStore):
         )
 
     def get_users_by_id_case_insensitive(self, user_id):
+        """Gets users that match user_id case insensitively.
+        Returns a mapping of user_id -> password_hash.
+        """
         def f(txn):
             sql = (
                 "SELECT name, password_hash FROM users"
-                " WHERE name = lower(?)"
+                " WHERE lower(name) = lower(?)"
             )
             txn.execute(sql, (user_id,))
-            return self.cursor_to_dict(txn)
+            return dict(txn.fetchall())
 
         return self.runInteraction("get_users_by_id_case_insensitive", f)