Drupal 8 REST - How to export Drupal 8 Main navigation menu with REST service (JSON)
I ended up creating a module that does the basics for getting a menu via rest. I can just put the menus machine name in the URL and it will give me the title, url and weight in JSON format. I uploaded it to github so you can test it out. It is by no means ready for productions web sites. I was just messing around with angular and REST in D8.

Using angular, I would get the menu using the new URL resource after enabling the module and route resource 'entity/restmenu/{menu-name}?_format=hal_json in your case entity/restmenu/main?_format=hal_json

app.controller('MainController', function($scope, $http) {
  $http.defaults.headers.common.Authorization = 'Basic YWRtaW46YWRtaW4=';
  $scope.menuData = $http.get('entity/restmenu/main?_format=hal_json').then(function(response) {
    $scope.menuData = JSON.parse(JSON.parse(response.data));
  });
});


https://github.com/rondog/rest-menu

&lt;?php

/**
 * @file
 * Contains \Drupal\rest_menu\Plugin\rest\resource\rest_menu.
 */

namespace Drupal\rest_menu\Plugin\rest\resource;

use Drupal\Core\Render\HtmlResponse;
use Drupal\Core\Menu;
use Drupal\Core\MenuTreeParameters;
use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Entity\EntityStorageException;
use Drupal\Core\Session\AccountProxyInterface;
use Drupal\rest\Plugin\ResourceBase;
use Drupal\rest\ResourceResponse;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
use Symfony\Component\HttpKernel\Exception\HttpException;
use Psr\Log\LoggerInterface;

/**
 * Provides a resource to get view modes by entity and bundle.
 *
 * @RestResource(
 *   id = "restmenu_resource",
 *   label = @Translation("REST Menu Resource"),
 *   uri_paths = {
 *     "canonical" = "/entity/restmenu/{menu}"
 *   }
 * )
 */
class RESTMenuResource extends ResourceBase {
  /**
   * A current user instance.
   *
   * @var \Drupal\Core\Session\AccountProxyInterface
   */
  protected $currentUser;

  /**
   * Constructs a Drupal\rest\Plugin\ResourceBase object.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin_id for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param array $serializer_formats
   *   The available serialization formats.
   * @param \Psr\Log\LoggerInterface $logger
   *   A logger instance.
   * @param \Drupal\Core\Session\AccountProxyInterface $current_user
   *   A current user instance.
   */
  public function __construct(
    array $configuration,
    $plugin_id,
    $plugin_definition,
    array $serializer_formats,
    LoggerInterface $logger,
    AccountProxyInterface $current_user) {
    parent::__construct($configuration, $plugin_id, $plugin_definition, $serializer_formats, $logger);

    $this-&gt;currentUser = $current_user;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static(
      $configuration,
      $plugin_id,
      $plugin_definition,
      $container-&gt;getParameter('serializer.formats'),
      $container-&gt;get('logger.factory')-&gt;get('rest'),
      $container-&gt;get('current_user')
    );
  }
  /**
   * Responds to GET requests.
   *
   * Returns a list of bundles for specified entity.
   *
   * @throws \Symfony\Component\HttpKernel\Exception\HttpException
   *   Throws exception expected.
   */
  public function get($entity) {
    $menu_name = $entity;
    $menu_parameters = \Drupal::menuTree()-&gt;getCurrentRouteMenuTreeParameters($menu_name);
    $tree = \Drupal::menuTree()-&gt;load($menu_name, $menu_parameters);
    $result = array();

    foreach ($tree as $element) {
      $link = $element-&gt;link;
      array_push($result, array(
          'title' =&gt; $link-&gt;getTitle(),
          'url' =&gt; $link-&gt;getUrlObject()-&gt;getInternalPath(),
          'weight' =&gt; $link-&gt;getWeight()
        )
      );
    }
    return new ResourceResponse(json_encode($result));
  }
}