code: protected function getSign()
      {
          if (is_null($this->userConfig->get('private_key'))) {
              throw new InvalidArgumentException('Missing Config -- [private_key]');
          }
          $res = "-----BEGIN RSA PRIVATE KEY-----\n" .
              wordwrap($this->userConfig->get('private_key'), 64, "\n", true) .
              "\n-----END RSA PRIVATE KEY-----";
          openssl_sign($this->getSignContent($this->config), $sign, $res, OPENSSL_ALGO_SHA256);
          return base64_encode($sign);
      }
docs: 获取数据签名
  @return string