滤器wp_nav_menu_objects 并将链接添加为项目，类似于this answer.

add_filter( \'wp_nav_menu_objects\', \'t5_menu_log_link\', 10, 2 );

/**
 * Add a link to the nav menu.
 *
 * @wp-hook wp_nav_menu_objects
 * @param  array  $sorted_menu_items Existing nav menu items
 * @param  object $args Nav menu arguments. \'add_loginout\' must be TRUE
 * @return array  Nav menu items
 */
function t5_menu_log_link( $sorted_menu_items, $args )
{
    $is_in                  = is_user_logged_in();

    $link                   = new stdClass;
    $link->title            = __( $is_in ? \'Log Out\' : \'Log In\' );
    $link->menu_item_parent = 0;
    $link->ID               = \'\';
    $link->db_id            = \'\';
    $link->url              = $is_in ? wp_logout_url() : wp_login_url();

    $sorted_menu_items[] = $link;

    return $sorted_menu_items;
}