KantSites/src/Controller/ConsentController.php

<?php

namespace App\Controller;

use App\Content\Consent;
use App\Content\SiteSettings;
use App\Content\Theme;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Attribute\Route;

/**
 * Recording and changing the consent decision.
 *
 * **No CSRF token here, deliberately.** The request changes nothing on the server: it sets a
 * cookie that only affects the browser that sent it. A token would need a session, and starting a
 * session for every visitor is exactly what a consent banner exists to avoid. What is checked is
 * the target of the redirect, so the form cannot be used to bounce someone to another site.
 */
final class ConsentController extends AbstractController
{
    public function __construct(private Consent $consent, private SiteSettings $settings, private Theme $theme)
    {
    }

    #[Route('/einwilligung', name: 'consent_save', methods: ['POST'])]
    public function save(Request $request): Response
    {
        $choice = $request->request->getString('choice');
        $groups = match ($choice) {
            'all' => array_keys(Consent::GROUPS),
            'none' => [],
            default => array_map(static fn (mixed $group): string => (string) $group, (array) $request->request->all('groups')),
        };
        $response = $this->redirect($this->backTo($request));
        // Eine Entscheidung trifft nur der eigene Browser auf dieser Website. Ein fremdes Formular,
        // das hierher postet, darf keine Einwilligung eintragen - die Route hat keine Sitzung und
        // damit kein CSRF-Token, also entscheidet die Herkunft der Anfrage.
        if ($this->sameSite($request)) {
            $this->consent->remember($request, $response, $groups);
        }

        return $response;
    }

    /** Ob die Anfrage von dieser Website kommt - nach dem, was der Browser darueber sagt. */
    private function sameSite(Request $request): bool
    {
        $site = $request->headers->get('Sec-Fetch-Site');
        if (null !== $site) {
            return \in_array($site, ['same-origin', 'same-site', 'none'], true);
        }
        $origin = $request->headers->get('Origin') ?? $request->headers->get('Referer');
        if (null === $origin || '' === $origin) {
            // Aeltere Browser nennen keine Herkunft; ohne Anhaltspunkt bleibt die Frage beantwortbar.
            return true;
        }
        $host = parse_url($origin, PHP_URL_HOST);

        return \is_string($host) && strtolower($host) === strtolower($request->getHost());
    }

    #[Route('/einwilligung', name: 'consent_page', methods: ['GET'])]
    public function page(Request $request): Response
    {
        if ([] === $this->consent->askedGroups()) {
            throw $this->createNotFoundException('Diese Website fragt nichts ab.');
        }
        // Deliberately without header and footer: this is a page about a decision, not a page of
        // the website, and it must work even when an area is broken.
        // Palette und Hinweisfarben wie auf den Seiten, damit die Entscheidung hier aussieht wie
        // die Frage dort. Das Stylesheet ist ueber seinen Hash erlaubt, nichts weiter.
        $theme = $this->theme->load();
        $styles = $this->theme->css($theme).$this->consent->styles($theme);
        $response = $this->render('consent.html.twig', [
            'consent' => $this->consent->state($request),
            'settings' => $this->settings->load(),
            'pageStyles' => $styles,
        ]);
        $response->headers->set('Cache-Control', 'no-store');
        $response->headers->set('X-Robots-Tag', 'noindex, follow');
        $response->headers->set('X-Content-Type-Options', 'nosniff');
        $response->headers->set('Referrer-Policy', 'strict-origin-when-cross-origin');
        // The page carries no embeds, so it keeps the strictest policy - plus the one hashed style block.
        $response->headers->set('Content-Security-Policy', sprintf("default-src 'self'; script-src 'none'; style-src 'self' 'sha256-%s'; img-src 'self' https: data:; object-src 'none'; base-uri 'none'; frame-ancestors 'none'; form-action 'self'", base64_encode(hash('sha256', $styles, true))));

        return $response;
    }

    /**
     * Back to where the form was submitted from, but only within this site: an open redirect
     * would turn a consent button into a way to send people anywhere.
     */
    private function backTo(Request $request): string
    {
        $target = $request->request->getString('back');
        // Nur ein Pfad dieser Website: `//fremd.example` ist protokollrelativ, und `/\fremd.example`
        // lesen Browser genauso.
        if ('' === $target || 1 !== preg_match('#^/(?![/\\\\])#', $target)) {
            return '/';
        }

        return $target;
    }
}