How can we alter/manage the links in toolbar user-menu?

In case anybody else stumbles upon this, I implemented the following to use a specific menu to populate the links in the toolbar.

function module_preprocess_links__toolbar_user(&$variables) {
  $menu_tree_service = \Drupal::service('menu.link_tree');
  $menu_name = 'user-toolbar';
  $parameters = new MenuTreeParameters();
  $parameters->setActiveTrail([$menu_name]);

  $main_tree_loaded = $menu_tree_service->load($menu_name, $parameters);
  $main_tree_built = $menu_tree_service->build($main_tree_loaded);

  // Note that this uses laravel collections, but you could do the same with a standard array_map
  $links = collect($main_tree_built['#items'])
    ->map(function (array $item) use ($variables) {
      return [
        'link' => [
          '#type' => 'link',
          '#title' => t($item['title']),
          '#url' => $item['url'],
        ],
        'text' => t($item['title']),
        'attributes' => $item['attributes'],
      ];
    });
  $variables['links'] = $links->toArray();
}