code: public function generateSecurityLink($domain, $path, $prefix, $secret)
      {
          $path = trim($path, Url::SEPARATOR);
          $prefix = trim($prefix, Url::SEPARATOR);
          $domain = rtrim($domain, Url::SEPARATOR);
  
          $hex = sprintf("%08x", time());
          $md5 = md5($secret . $path . $hex);
  
          return sprintf('%s/%s/%s/%s/%s', $domain, $prefix, $md5, $hex, $path);
      }
docs: Return security link for mod_secdownload lighttpd.
  http://redmine.lighttpd.net/projects/1/wiki/Docs_ModSecDownload
  
  @param string $domain
  @param string $path
  @param string $prefix
  @param string $secret
  @return string