Decision sorb. Measured basis rather than preference: four months of operation with
zero destinations, zero remote users and zero rooms with outside participation, while
the federation API answered publicly - the delegation routes it over 443, so 8448
being shut never mattered.
An empty list federates with nobody and one entry opens it for exactly that domain,
so the capability stays one line away rather than gone.
The comment records what must not be done instead, because it is not obvious and it
would look correct: blocking /_matrix/federation at the edge. lk-jwt-service verifies
OpenID tokens through /_matrix/federation/v1/openid/userinfo and reaches it over the
public name - no hostAliases, ClusterFirst DNS - so a path-level block kills group
calls. Synapse serves that endpoint without an X-Matrix signature, so the whitelist
does not touch it.
Caught while validating: the first version of this edit split the auto_join block,
moving auto_join_rooms_for_guests under federation. Functionally identical after the
fragments merge, wrong to read, and fixed before pushing - the diff is now 20 added
lines and nothing moved.
Thore Cimbal
3935f359f9