Keycloak and Better Auth aren't as fundamentally different as you may think! Better auth supports authn/z, being an identity _source_, being an identity provider, being an OIDC/SSO provider (so others can login using better auth), rbac, SAML/SCIM, and a ton more. It's actually really powerful! Most folks found better auth as an alternative to next-auth/auth.js - but better auth does a lot more than those.

(some of those features are enterprise only)