Proxy authentication method should auto create new user

[DavisGoglin]

Is your feature request related to a problem? Please describe.

When using proxy authentication, each user that uses this app needs an account pre-created. That user also needs a password assigned that will never be used.

Describe the solution you'd like

When in proxy authentication mode and a user logs in via a header without an existing account, filebrowser should (optionally?) create that user with a blank/random password and user settings based on the default security settings.

Describe alternatives you've considered

• Using a static or group based header to login to a generic user in filebrowser. This loses per-user permission options, but if the header can be modified from the auth proxy on a user-group basis then this gets close.
• API to auto-create users.

Additional context

When enabling the proxy authentication setting and logged in with a user that doesn't exist, there is nothing in the logs to diagnose this besides a 403. Additional logging showing the auth mode and the attempted username would be helpful.

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[github-actions]

This issue was closed because it has been stalled for 5 days with no activity.