[Feature Request] Accepting authentication headers from a service like Authelia

[BlayW]

It'd be nice if I could use my server's centralised authentication to sign in to KaraokeEternal. This would involve:

• identity headers
• a shared secret header from the proxy
• we'd need to match users using email (probably?)
• create new users on a new login from the proxy
• map a proxy group to the KaraokeEternal admin group
• maintain local login functionality even when proxy login it enable (as a backup)

Full OIDC support is another can of worms, but think at minimum accepting trusted headers from the proxy is doable