code: public function verify($data, $sign = null, $sync = false)
      {
          $data = $this->fromXml($data);
          $sign = is_null($sign) ? $data['sign'] : $sign;
          return $this->getSign($data) === $sign ? $data : false;
      }
docs: XML内容验证
  @param string $data
  @param null $sign
  @param bool $sync
  @return array|bool