Login cookie errors tracker

track-login-cookie-errors.php

<?php
/**
 * Plugin name: Login cookie errors tracker
 * Description: Trigger error when test cookie on login page issue occurs
 * Author: Paweł Kopociński
 * Version: 2022.09.27
 */

defined( 'ABSPATH' ) || exit;

/**
 * Logs the test cookie error.
 *
 * Warning level of reporting is used, because of issues with reporting levels in different environments.
 *
 * @since 2022.09.27
 * @see https://github.com/WordPress/WordPress/blob/b0ebbf6bebb9a24a310416fc62d85b567171144a/wp-login.php#L1231-L1267
 * @see https://cxlworld.slack.com/archives/C01JABH8AHX/p1664207160644329
 * @see https://app.clickup.com/t/37pta7h
 */
add_filter( 'login_redirect', static function( $redirect_to, $requested_redirect_to, $user ): string {
    /** @var WP_Error|WP_User $user */
    if ( is_wp_error( $user ) && 'test_cookie' === $user->get_error_code() ) {
        trigger_error( $user->get_error_message( 'test_cookie' ), E_USER_WARNING );
    }

    return $redirect_to;
}, 10, 3 );