Protocol-wise, OIDC is generally the most supported out there. LDAP too, to an extent.

Software wise, I find Kanidm quite simple to set up (basically just one container). It’s mostly managed via the terminal though, and lacks some eyecandy. But some of the examples in its docs should be easy to follow and get you familiar with mapping scopes/groups between Kanidm and services.

Authelia is okay too