TYPO3 Core

Just had to debug why my custom header did not end up in response.

<?php

namespace MyClient\MyExt\Controller;

use Psr\Http\Message\ResponseInterface;
use TYPO3\CMS\Core\Http\JsonResponse;

class DemoController extends AbstractController
{
    public function ajaxAction(): ResponseInterface
    {
        return new JsonResponse([], 200, ['X-Page' => 123]);
    }
}

The header will be skipped due to hard checks on the correct type and does not throw any notice in `\TYPO3\CMS\Core\Http\Message::filterHeaders`.

It would be nice to:

- get a notice thrown on invalid headers, easing the developer experience
- allow header values to go through https://www.php.net/manual/de/function.strval.php, therefore allowing any string representation of a given value and the support for classes that implement https://www.php.net/manual/de/class.stringable.php.