private function calculateHeader(array $parameters, $url)
        {
            // divide into parts
            $parts = parse_url((string) $url);

            // init var
            $chunks = array();

            // process queries
            foreach ($parameters as $key => $value) {
                $chunks[] = str_replace(
                    '%25', '%',
                    self::urlencode_rfc3986($key) . '="' . self::urlencode_rfc3986($value) . '"'
                );
            }

            // build return
            $return = 'Authorization: OAuth realm="", ';
            $return .= implode(',', $chunks);

            // prepend name and OAuth part
            return $return;
        }