keycloak can broker between identity providers. It can use social logins as identity providers, connect to ldap, kerberos and others for user federation, and then provide SAML and OpenIDC to other applications.
We have also added an event plugin to keycloak to push login events to a queue for other services to consume.
We also offer local keycloak identities in case a customer does not or can not provide their own identities, and have added haveibeenpwnd logic to check password strength/reuse for these local keycloak identities.
I am rebuilding my homelab soon and I am interested in having centralized auth across all systems and as many applications as feasible, using my centralized fileserver as an IDP source via some application or another, as well as using Keycloak for some one-off projects where I don't really want to write a user layer.