Devise\Users\UserManager::createRules PHP Method

    public function createRules()
    {
        return array('email' => 'required|email|unique:users', 'username' => 'required|unique:users', 'password' => 'required|min:6', 'password_confirmation' => 'required|min:6|same:password', 'group_id' => 'required|exists:groups,id');
    }