public boolean grantModeratorRole(String uid) throws Exception {
  FirebaseAuth auth = FirebaseAuth.getInstance();
  UserRecord user = auth.getUserAsync(uid).get();
  if (user.isEmailVerified()) {
    Map<String, Object> claims = new HashMap<>();
    claims.put("role", "moderator");
    claims.put("level", 5);
    auth.setCustomUserClaimsAsync(uid, claims).get();
    return true;
  }
  return false;
}