Would be great if basic http authentication could be used to authenticate users.

With SSO systems like Authentik you can use forward-auth to delegate authentication to the SSO system.
It can then send custom headers to the application which can use those headers to authenticate as a specific user.

In forward-auth scenario either a custom x-forwarded-username header can be used (which is injected by the forward-auth mechanism), or a basic http authentication could be used (credentials are injected by the forward-auth mechannism).

Backrest seems to use bearer authentication which would not work with Authentik.
So either supporting basic auth or defining header with the username would be great addition to support SSO forward-auth.