We talked a bit about FederationBase calling a FederationClient method on Matrix, wanted to capture the results from rich:

I'm pretty sure I decided that FederationServer.on_query_auth_request had been broken forever and needed to die, which means that _check_sigs_and_hash_and_fetch can move to FederationClient
some more context: _on_query_auth_request implements an undocumented, unused REST endpoint

Originally posted by @clokep in #6996 (comment)