Don't you use Keycloak for SSO? The ports needed for that needs to be accessible so services can talk to it. If there's a dedicated port for management you can still use it with software like pangolin. Run the management service on only a local port and access using this software or wireguad.
I use authentik and as far as I know the management is on the same web port so I have to allow some paths to be accessible to the world.
> So I am wondering if I can reduce attack surface by making "management" services (Keycloak admin console, the headless CMS admin interface etc.) accessible only to me...
The answer to this is YES. Of course there are a variety of ways to implement. In your case I would start simple with something like wireguard. Keycloak won't be easy to install and configure as a beginner. If your needs are simple, check out https://github.com/lldap/lldap for authentication (and user management).
I'm not using anything YET. I am thinking about hosting a pepper variety database I am developing on a VPS for public use. I want to use Keycloak for authentication and also some other services alongside (eg. a headless CMS for writing some of the content).
The thing is, I don't have any prior experience with hosting at all. So I am wondering if I can reduce attack surface by making "management" services (Keycloak admin console, the headless CMS admin interface etc.) accessible only to me...