docs: public static void flattenCookies(final HttpServerExchange exchange) {
          Map<String, Cookie> cookies = exchange.getResponseCookiesInternal();
          boolean enableRfc6265Validation = exchange.getConnection().getUndertowOptions().get(UndertowOptions.ENABLE_RFC6265_COOKIE_VALIDATION, UndertowOptions.DEFAULT_ENABLE_RFC6265_COOKIE_VALIDATION);
          if (cookies != null) {
              for (Map.Entry<String, Cookie> entry : cookies.entrySet()) {
                  exchange.getResponseHeaders().add(Headers.SET_COOKIE, getCookieString(entry.getValue(), enableRfc6265Validation));
              }
          }
      }