Use OAuth.xyz

[jaxoncreed]

Notes from Justin Richer

The current OIDC use in Solid required dynamic registration which, for the Solid use case, is an unneeded step. https://oauth.xyz/ might be a better fit

[elf-pavlik]

I think everyone had chance to take a look at it. Let's close this issue and if needed we can follow up with some specific proposals inspired by oauth.xyz.