Maintenance Mode

<?php

add_action( 'template_redirect', function () {
    $secret_pass = 'go';
    $maintenance_url = '/under-construction/';
    $protocol = 'https://';
    $user_is_admin = current_user_can( 'manage_options' );

    if ($user_is_admin) return;

    if ( ($_GET ['access'] ?? "") === $secret_pass ) return;

    $path = $_SERVER[ 'REQUEST_URI' ];

    if ( $path !== $maintenance_url ) {
        exit ( wp_redirect( home_url( $maintenance_url), 307 )) ;
    }
});