I don't have a simple guide, but it's probably a good idea to reduce the number of moving parts if you're trying to keep stuff simple. So pick something that has all the features in-one (user management, authentication, authorization, ...). They might not be the best at ever single thing (they almost certainly won't), but doing it all usually means that it's easier to configure and you don't need to wire multiple things together.
I've recently moved from Authelia to Authentik due to some features that I was missing/wishing for, but between those two I'd definitely say Authenlia is easier to get running initially (and you don't need external LDAP for it, as others have mentioned).
You'll probably still need a proxy that can do proxy auth because not all services can do OICD/OAuth2. I'm using Traefik, but heard that Caddy is easier to set up initially (can't compare myself).