code: public function onBuild(MenuEvent $event): void
      {
          $token = $this->tokenStorage->getToken();
  
          if (null === $token) {
              return;
          }
  
          $user = $token->getUser();
  
          if (!$user instanceof BackendUser) {
              return;
          }
  
          $factory = $event->getFactory();
          $tree = $event->getTree();
          $modules = $user->navigation();
  
          foreach ($modules as $categoryName => $categoryData) {
              $categoryNode = $tree->getChild($categoryName);
  
              if (!$categoryNode) {
                  $categoryNode = $this->createNode($factory, $categoryName, $categoryData);
  
                  if (isset($categoryData['class']) && preg_match('/\bnode-collapsed\b/', $categoryData['class'])) {
                      $categoryNode->setDisplayChildren(false);
                  }
  
                  $tree->addChild($categoryNode);
              }
  
              // Create the child nodes
              foreach ($categoryData['modules'] as $moduleName => $moduleData) {
                  $moduleNode = $this->createNode($factory, $moduleName, $moduleData);
                  $moduleNode->setCurrent((bool) $moduleData['isActive']);
  
                  $categoryNode->addChild($moduleNode);
              }
          }
      }
docs: Adds the back end user navigation.