Authentication

    private void onAuthSuccess(FirebaseUser user) {
        String username = usernameFromEmail(user.getEmail());

        writeNewUser(user.getUid(), username, user.getEmail());
    }

    private void writeNewUser(String userId, String name, String email) {
        User user = new User(name, email);

        mDatabase.child("USERS").child(userId).setValue(user);
    }