public function login($username = null, $password = null)
    {
        if (!isset($username) && isset($_POST['username'])) {
            $username = $_POST['username'];
        }
        if (!isset($password) && isset($_POST['password'])) {
            $password = $_POST['password'];
        }

        $result = $this->request('POST', 'login', compact('username', 'password'));
        $this->userinfo = $result;

        return $this->userinfo;
    }