in fact, RoR free version secures only elasticsearch, not kibana.
but, as limiting access to data in elasticsearch, you can limit access to data through kibana by the same way.
if you want security enforcement on kibana, you should look for pro version at least.
you ll get ride of basic mode authentication, and also will be able to secure kibana content like dashboard and co.
You should see the difference between version in https://readonlyrest.com/#chart