I built a little prototype [0] for script based authenticators inspired by a discussion on the keycloak-users mailing list -
think it was about post broker authentication checks, e.g. if the user has an email address that belongs to the google apps domain...
I introduced a ScriptBasedAuthenticator that is bootstraped via a
ScriptBasedAuthenticatorFactory can be execute a configured script
via a JSR-223 ScriptEngine against a provided execution context.
I also added a new "script" value type for proper rendering in the UI as well as an alias property
to the AuthFlowExecutionRepresentation in order to be able to differentiate multiple instances of an Authenticator
within the same AuthFlow - this comes pretty close to having Auth0 like scriptable rules in Keycloak.
For convenient editing I added the AngularJS bindings for the popular ACE editor.