code: public function encrypt($data)
      {
          if ($this->key === false) {
              return '';
          }
  
          $res = openssl_get_privatekey($this->key);
          if (empty($res)) {
              throw new \Exception('您使用的私钥格式错误，请检查RSA私钥配置');
          }
  
          openssl_sign($data, $sign, $res, OPENSSL_ALGO_SHA256);
          openssl_free_key($res);
  
          //base64编码
          $sign = base64_encode($sign);
          return $sign;
      }
docs: RSA2签名, 此处秘钥是私有秘钥
  @param string $data 签名的数组
  @throws \Exception
  @return string
  @author helei