CVE-2022-31152: Denial of service due to incorrect application of event authorization rules

The Matrix specification specifies a list of event authorization rules which must be checked when determining if an event should be accepted into a room.

In versions of Synapse up to and including v1.61, some of these rules are not correctly applied. An attacker could craft events which would be accepted by Synapse but not a spec-conformant server, potentially causing divergence in the room state between servers.