Feature Request: allow authentication by HTTP header (for oauth2-proxy integration)

[landure]

Problem Statement

I'm using OAuth2-Proxy to manage my users access to most apps. It pass the user authentication information via HTTP headers

Proposed Solution

It would be nice to support authentication by (customizable) HTTP headers, with automatic user creation if user signup as described in #244 is on.

This would add support for SSO solutions such as OAuth2-Proxy, …

Alternatives Considered

No response

Additional Context

No response