`/.well-known/webfinger` endpoint

[azmeuk]

The OpenID Connect discovery specification second paragraph is about issue domain discovery based on the RFC7033 webfinger.

Would it be relevant for authlib to provide helpers to implement this endpoint?

The main issue I can see is that this endpoint must be served at the top domain (i.e. mydomain.tld if the IDP is served at auth.mydomain.tld), but this can easily be solved with some webserver proxying configuration.