WP Maintenance mu-plugin - redirect to login page

maintenance-mode.php

<?php
// Exit if accessed directly
if ( !defined('ABSPATH') ) exit;

/**
 * Plugin Name: Maintenance mode
 * Description: maintenance mode.
 * Author: EDL
 * Author URI: 
 * Version: 1.1
 */

// Redirect to login page if user is not logged in
function activate_maintenance_mode() {
  auth_redirect();
}
/* Hooks the 'activate_maintenance_mode' function on to the 'template_redirect' action. */
//if( WP_ENV == "staging" || WP_ENV == "production" ) {
if( WP_ENV == "staging" ) {
  add_action('template_redirect', 'activate_maintenance_mode');
}