Not sure if I am doing something wrong but using this api https://www.firebase.com/docs/security/simple-login-email-password.html I can successfully create a user - accordin
When using email / password authentication in Firebase Authentication (previously known as Firebase SimpleLogin), your user's email and password combination is securely stored separately from the data actually stored in your Firebase.
This barrier between the data in your Firebase and your users' email / password hash combinations is by design: we want to make it easier for you to (1) develop your application, (2) prevent any accidental user credential leaks, and (3) still give you total flexibility with how to store your user data in Firebase.
That means that we only store the email address / password hash combination and nothing else, so it is up to you to decide how to store actual user data in your Firebase. As you suggested, you should be taking the user id and storing that data in your Firebase in a location such as /users/$id, and using the Firebase Security Rules Language to determine read / write access to that data. Your user's unique id and email are already in the auth variable you'll use when writing rules.