class LoginLogoutMenuLink

class LoginLogoutMenuLink extends MenuLinkDefault {
    
    /**
     * The current user.
     *
     * @var \Drupal\Core\Session\AccountInterface
     */
    protected $currentUser;
    
    /**
     * Constructs a new LoginLogoutMenuLink.
     *
     * @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 \Drupal\Core\Menu\StaticMenuLinkOverridesInterface $static_override
     *   The static override storage.
     * @param \Drupal\Core\Session\AccountInterface $current_user
     *   The current user.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, StaticMenuLinkOverridesInterface $static_override, AccountInterface $current_user) {
        parent::__construct($configuration, $plugin_id, $plugin_definition, $static_override);
        $this->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->get('menu_link.static.overrides'), $container->get('current_user'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTitle() {
        if ($this->currentUser
            ->isAuthenticated()) {
            return $this->t('Log out');
        }
        else {
            return $this->t('Log in');
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRouteName() {
        if ($this->currentUser
            ->isAuthenticated()) {
            return 'user.logout';
        }
        else {
            return 'user.login';
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheContexts() {
        return [
            'user.roles:authenticated',
        ];
    }

}