Comment by Arathorn

That's .well-known based delegation, which was proposed in MSC1708 in Nov 2017: https://github.com/matrix-org/matrix-spec-proposals/blob/old... and merged into the spec in Jan 2019 (prior to Matrix 1.0 in June 2019): https://github.com/matrix-org/matrix-spec/commit/0347e873efc...

So yes, fully-baked and part of Matrix since 1.0!

Next Gen Auth via OIDC is instead a key part of the (upcoming) Matrix 2.0 spec release - see https://areweoidcyet.com and https://github.com/matrix-org/matrix-spec-proposals/pull/386...