code: public static function getHeaderSign($serviceConfig, $method, $path, $contentMd5 = null)
      {
          $gmtDate = gmdate('D, d M Y H:i:s \G\M\T');
  
          $policy = null;
          $sign = self::getBodySignature($serviceConfig, $method, $path, $gmtDate, $policy, $contentMd5);
  
          $headers = array(
              'Authorization' => $sign,
              'Date' => $gmtDate,
              'User-agent' => 'Php-Sdk/' . $serviceConfig->getVersion()
          );
          return $headers;
      }
docs: 获取 Header 签名需要的请求头
  
  @param Config $serviceConfig
  @param $method 请求方法
  @param $path  请求路径
  @param $contentMd5 文件内容 md5
  
  @return array