Respond in JSON for URL's below API if 404

Fixes #2685.

Author: nickygerritsen

webapp/src/EventListener/RespondInJsonForApiListener.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types=1);
+
+namespace App\EventListener;
+
+use Symfony\Component\EventDispatcher\Attribute\AsEventListener;
+use Symfony\Component\HttpKernel\Event\ControllerEvent;
+
+#[AsEventListener]
+class RespondInJsonForApiListener
+{
+    public function __invoke(ControllerEvent $event): void
+    {
+        // For API requests, if no accept header has been set, or it is text/html or */*,
+        // set it to application/json.
+
+        $request = $event->getRequest();
+        if ($request->attributes->get('_fos_rest_zone')) {
+            $acceptHeader = $request->headers->get('accept');
+
+            if (!$acceptHeader
+                || str_starts_with($acceptHeader, 'text/html')
+                || str_starts_with($acceptHeader, '*/*')) {
+                $request->headers->set('accept', 'application/json');
+            }
+        }
+    }
+}