title: Single sign on using only Firebase
body: <p>I have two domains using the same Firebase backend instance. We are using Firebase Email &amp; Password auth only (we have no backend). Is it possible to allow users to roam between domains without forcing them to login again? One thought is that when a logged in user is redirected to the other domain, we pass the JWT in the URL, then use it to automatically login on the other domain. Would that be workable? Are there any security concerns there?</p>