Domino uses Keycloak authentication service that runs in a pod on your Domino cluster and is used to view, create, and manage groups of users. See the official Keycloak documentation for details.
You can access the Keycloak instance on any Domino cluster at https://<your-domino-domain>/auth/. You must sign in to the Keycloak admin console at least once to initialize the authentication service.
Enable user registration from the Keycloak console so users can sign up to join your fresh Domino install.
Keycloak offers several user authentication methods: