code: public function normalizeHeaders($params)
      {
          $out = '';
  
          foreach ($params as $key => $param) {
              $out .= $key.'="'.rawurlencode(trim($param)).'",';
          }
  
          return rtrim($out, ',');
      }
docs: Transforms a parameters array into
  a series of strings compatible to be
  embedded in a request header.
  
  @param array $params
  
  @return string