Start implementing auth conflict res

synapse/storage/rejections.py

@@ -31,3 +31,13 @@ class RejectionsStore(SQLBaseStore):
                 "last_failure": self._clock.time_msec(),
             }
         )
+
+    def get_rejection_reason(self, event_id):
+        self._simple_select_one_onecol(
+            table="rejections",
+            retcol="reason",
+            keyvalues={
+                "event_id": event_id,
+            },
+            allow_none=True,
+        )