We used keycloak at the Accelerator I worked for. I used it to provide auth and SAML SSO to enterprises while giving our devs an easy to integrate module. It worked great. Theming the login/signup/forgot password pages was simple and easy but would have been easier for the teams if it was React. Nevertheless we built some amazing B2B SaaS software using Keycloak as our identity provider.

I would use it again for sure.