MAPG-191 don't create separate variable for data where not necessary

public/index.php

@@ -26,8 +26,9 @@ if ($match !== null) {
     }
 
     if ($method === 'post' && Container::$request->post('anti_csrf_token') !== Container::$request->session()->get('anti_csrf_token')) {
+        $content = new MapGuesser\Response\JsonContent(['error' => 'no_valid_anti_csrf_token']);
         header('Content-Type: text/html; charset=UTF-8', true, 403);
-        echo json_encode(['error' => 'no_valid_anti_csrf_token']);
+        $content->render();
         return;
     }