Allow limiting users based on userinfo

[ajmyyra]

Currently every user able to login at OIDC endpoint will be let in. Make it possible to limit users, for example with email domain or if their email_verified is set to true.

[travisghansen]

Inspired by this and other projects, I started a generic external auth service that I'd be interested to have your feedback on: https://github.com/travisghansen/external-auth-server

I haven't specifically added assertions based on userinfo yet, but I'm real close. I'd love another set of eyes if you have any interest.

[ajmyyra]

Looks cool, really great to have more generic approach to the issue! I'll take a look in a few days when I've got time (just got back from vacation, so jetlag is a thing :)

[travisghansen]

Great! Assertions have been implemented now for both id_token and userinfo data..