code: public static function getBodySignature(Config $serviceConfig, $method, $uri, $date = null, $policy = null, $contentMd5 = null)
      {
          $data = array(
              $method,
              $uri
          );
          if ($date) {
              $data[] = $date;
          }
  
          if ($policy) {
              $data[] = $policy;
          }
  
          if ($contentMd5) {
              $data[] = $contentMd5;
          }
          $signature = base64_encode(hash_hmac('sha1', implode('&', $data), $serviceConfig->operatorPassword, true));
          return 'UPYUN ' . $serviceConfig->operatorName . ':' . $signature;
      }
docs: 获取表单 API 需要的签名，依据 body 签名规则计算
  @param Config $serviceConfig
  @param $method 请求方法
  @param $uri 请求路径
  @param $date 请求时间
  @param $policy
  @param $contentMd5 请求 body 的 md5
  
  @return array