absolute URLs with domain instead of just absolute from root dir

We have a website where multiple subsites (with different (sub-)domains) belong. These subsites are external systems which request the header and footer of the main site and put it into their sides. As the domain for the subsites is different all references from the header/ footer needs to include the domain of the main site.

This is done with config.absRefPrefix = https://www.maindomain.tld/

As we just updated that site from TYPO3 9 to TYPO3 11 (no longer realurl) we noticed:
the main-domain no longer is in the generated URL of the menu links. All links are just links starting with the root dir / - which do not exist on the subsites.

The links are generated with the VH f:link.typolink from a field with renderType = inputLink which just holds a page-id.

Why is the configuration config.absRefPrefix ignored by the VH? (images does contain the domain!)

What needs to be changed to get the domain in the generated links?

Our current solution is a text replace of the relative links to absolute links. But I'm not happy with it.

The absRefPrefix has somehow been deprecated since the implementation of the siteconfig in TYPO3 9.

See: https://forge.typo3.org/issues/87919

TYPO3 >= 12
You can set following in your TypoScript setup:

config.forceAbsoluteUrls = true

TYPO3 < 12
You can set following in your TypoScript setup:

typolink.forceAbsoluteUrl = true

If that does not fits your requirements, then you could also implement a middleware. I had to adjust the middleware in the above bugreport to get it working. To do so:

Register the middleware in your sitepackage Configuration/RequestMiddlewares.php:

<?php
return [
    'frontend' => [
        'sitepackage-abs-ref-prefix-' => [
            'target' => VENDOR\ExtName\Middleware\AbsRefPrefixEnforcer::class,
            'before' => [
                'typo3/cms-redirects/redirecthandler'
            ],
            'after' => [
                'typo3/cms-frontend/site',
            ]
        ]
    ]
];

And then implement the middleware Classes/Middleware/AbsRefPrefixEnforcer.php:

<?php
namespace VENDOR\ExtName\Middleware;

use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Server\MiddlewareInterface;
use Psr\Http\Server\RequestHandlerInterface;
use TYPO3\CMS\Core\Http\NullResponse;
use TYPO3\CMS\Core\Http\Stream;
use TYPO3\CMS\Frontend\Controller\TypoScriptFrontendController;

/**
 * prefix all links and src with $GLOBALS['TSFE']->absRefPrefix
 *
 * Class GenerateAbsoluteLinksMiddleware
 * @package Clickstorm\CsNewsletterExport\Middleware
 */
class AbsRefPrefixEnforcer implements MiddlewareInterface
{

    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
    {

        $response = $handler->handle($request);
        if (
            !($response instanceof NullResponse)
            && $GLOBALS['TSFE'] instanceof TypoScriptFrontendController
            && $GLOBALS['TSFE']->absRefPrefix
            && $GLOBALS['TSFE']->absRefPrefix !== '/'
            && $GLOBALS['TSFE']->absRefPrefix !== 'auto'
        ) {
            $body = $response->getBody();
            $body->rewind();
            $contents = $response->getBody()->getContents();
            $content = $this->parseRelativeToAbsoluteUrls($contents);
            $body = new Stream('php://temp', 'rw');
            $body->write($content);
            $response = $response->withBody($body);
        }

        return $response;
    }

    protected function parseRelativeToAbsoluteUrls(string $input = ''): string
    {
        // https://thydzik.com/convert-relative-links-to-absolute-links-with-php-regex/
        $prefix = $GLOBALS['TSFE']->absRefPrefix;
        return preg_replace('/((?:href|src) *= *[\'"])(\/)/i', "$1$prefix", $input);
    }
}