Support for X-Forwarded-Groups

[fnpanic]

Hi,

when using a reverse proxy out it works great with script server to pass the X-Forwarded-User.

oauth2_proxy can also pass X-Forwarded-Groups which would be great to be used similar to ldap. https://oauth2-proxy.github.io/oauth2-proxy/docs/configuration/overview

This would open the auth to almost any provider. Also using vouch proxy https://github.com/vouch/vouch-proxy has the same behavior and uses the nginx request module (claims). (just different names for the headers).

Having a general way to use auth with users and groups would be awesome.