Consider custom support for authentication

[cezaraugusto]

Authenticating extensions with mainstream auth tools/platforms is surprisingly complex. Extension.js could have use/have some abstraction tool to make it easier to authenticate extensions with existing platforms/webapps.

I'd like to see what others think/use for this. At the moment of this writing there is one request for Supabase support in Extension.js (see discussion), but unlike Firebase, there seems to have no official support for authenticating extensions with their platform, so we'd need to either create a lib or patch existing user alternatives.