Add full OAuth2 capabilities to SSO service

[humphd]

We're working on providing admin OAuth2 services via GitHub, oauth2-proxy, etc. and it makes me think that we should consider extending our SSO service so that it provides a full OAuth2 feature set.

To do that, we would add one of these:

• https://github.com/jaredhanson/oauth2orize
• https://github.com/oauthjs/node-oauth2-server

I have never tired this, but I think it should be doable. Once we had this, we could use our SSO services for any OAuth2 needs with our apps (Portainer, Supabase, Docker, etc).