Authelia is an open-source authentication and authorization server providing
2-factor authentication and single sign-on (SSO) for your applications via a
web portal. It acts as a companion of reverse proxies like nginx, Traefik or
HAProxy to let them know whether queries should pass through. Unauthenticated
users are redirected to Authelia Sign-in portal instead.

WWW: https://www.authelia.com/docs/