OAuth2-Proxy support for authentication

[jared252016]

Add support for OAuth2-Proxy and proxy_auth as an authentication method, with API support.

This is extremely easy to do if doable per proxy-host, but setting up auth like instead of basic auth would be ideal.

[LeonardoIz]

For authentication it is better to use Authelia or Authentik, both work very well with npm

[phulstaert]

Most people won't change their current authentication system because they want to use npm.
Authentik uses a proxy provider that works with npm (although they have a huge error in their config)

It would be wise to implement the OAuth2 authentication protocol for access to npm itself AND access to subdomains.
A good and easy implementation would 'lure' a lot of SSO users.

[phulstaert]

I also see there is a "openidc" branch with nice gui support. A real pitty this is not documented or integrated in the latest release. Now you have to choose between the latest updates or OpenID Connect Support