wp-securiser-access-wp-admin-wp-login-cookie-personnalise.php

<?php
add_action('init', 'hwk_login_cookie', 0);
function hwk_login_cookie(){
    global $pagenow;
    if((!is_admin() && $pagenow != 'wp-login.php') || wp_doing_ajax() || (defined('DOING_AJAX') && DOING_AJAX === true))
        return;
    
    $rule = array(
        'key'   => 'ma_clef',
        'value' => 'ma_valeur'
    );
    if( !isset($_COOKIE[$rule['key']]) || empty($_COOKIE[$rule['key']]) || $_COOKIE[$rule['key']] != $rule['value'] ){
        wp_redirect(home_url());
        exit;
    }
}