How do I set up roles in firebase auth?

I am currently logging in with email and password. But I would like to be able to assign a role to each user: admin or user. I have read that this is done by using the custom auth method, but I find the docs not clear to implement with email/password authentication.

How would I go to set that up?

I am currently using firebase for ember emberfire

Update:

Docs reference: http://ift.tt/1DsuwVN