code: public static function buildAuthString(array $data)
      {
          $str = array();
  
          foreach ($data as $k => $v) {
              $str[] = self::urlEncode($k) . '="' . self::urlEncode($v) . '"';
          }
  
          return implode(', ', $str);
      }
docs: Build the string that we use in the authentication header
  
  @param array $data
  @return string