Generalized authentication

[mboisson]

• Make staff and access attributes configurable for all authentication classes
• Ensure no error is issued in authentication.py because a package is not installed by wrapping imports and class definitions in try/except clauses
• Implement support for authentication with OIDC
• Implement support for authentication with OAuth2 + JWT tokens
• Implement a middleware to handle when multiple proxies are used so that forwarded headers are understood correctly by the OIDC authentication layer

This PR supersedes #118

Code co-written with Google Antigravity.