@cicnavi @monkeyiq First look?
I think it's already a huge improvement and we could for example fix #2643 with this.

Idea:

I have left out the migration to PSR-17 to interact with the saml2-lib (see old PR)..
We can easily re-introduce this by backporting the saml2-bindings from saml2v6 into samlv4

Edit: Never mind, I see now that Template here is XHTML/Template and so is a response.

Looking at this, modules/admin/src/Controller/Config.php still falls through to the code that does

        return $this->menu->insert($t);

Which by looking at Menu should be then trying to return a Template object from Config diagnostics and main.

Looking at #1760 it doesnt seem there was a Menu.php update there to be picked still.

I will go back to reading and using emacs to make cross check comments before posting to avoid noise

I have read over most of this now. I have not checked it out and run it yet.

NB: This is more of a comment for a future update if we like the idea.

One thought I had was to do with getting query parameters...

$consumerURL = null;
if ($request->query->has('ConsumerURL')) {
    $consumerURL = $request->query->get('ConsumerURL');
}

Looking at the symfony source code it seems that this could be a single line. Though the temptation there is also to use the FILTER to validate things at that time as well. (https://github.com/symfony/symfony/blob/e9a41cc7483070563d0e8264842e064716319e11/src/Symfony/Component/HttpFoundation/InputBag.php#L143)

$consumerURL = $request->query->filter( 'ConsumerURL', null );

Looking at the symfony source code it seems that this could be a single line.

I'm trying to not change anything in this already huge PR that is not related to passing requests/responses back and forth. Also, I would never use ->filter(.., null) because it gives a false sense that we're filtering something when we don't.. Reducing the if/has/get to a oneliner makes sense here.