Love Gentoo. Being using it for 20+ years and never looked back.
Using also CentOS for work, and would switch to Gentoo if I could.
Really, gentoo for everything (from laptop to headless server), but not for where a rolling release distro is not suitable (configuration control and such needs).
They actually do, i am down the same path recently and installing authelia was the best choice I made. Still working on it.
But most stvies support either basic auth, headers auth, oidc or similar approaches. Very few don't.