You've always been able to run a Matrix server completely separately from the wider federation, and there are loads of them out there (we estimate around 35,000

You've always been able to run a Matrix server completely separately from the wider federation, and there are loads of them out there (we estimate around 35,000). Unsure what "federated" authentication problem you're thinking of. The only thing I can think that you're referring to is the question of how you track the keys used by servers to sign the events they send. If the server is offline, and you've never heard of it before, you still need a way to check their key. We don't currently use CAs for this, but instead you grab a cached copy of the key from a trusted server: https://github.com/matrix-org/synapse/blob/a743bf46949e851c9a10d8e01a138659f3af2484/docs/sample_config.yaml#L1431-L1471 https://github.com/matrix-org/synapse/blob/a743bf46949e851c9.... This is a bit of an edge case, as in general servers whose events you care about will typically still be online - or you'll know their signing key back from when they were on line. The longer term solution for this is https://github.com/matrix-org/matrix-doc/blob/rav/proposal/remove_mxids_from_events/proposals/1228-removing-mxids-from-events.md https://github.com/matrix-org/matrix-doc/blob/rav/proposal/r... which includes the sender's public key in the event (by making it the sender's identity) - and we're working on this as part of P2P Matrix currently.