code: protected function makeSign($signStr)
      {
          switch ($this->signType) {
              case 'MD5':
                  $signStr .= '&key=' . $this->md5Key;
                  $sign = md5($signStr);
                  break;
              case 'HMAC-SHA256':
                  $sign = base64_encode(hash_hmac('sha256', $signStr, $this->md5Key));
                  break;
              default:
                  $sign = '';
          }
          return strtoupper($sign);
      }
docs: 签名算法实现  便于后期扩展微信不同的加密方式
  @param string $signStr
  @return string