CronAccessCheck.php

<?php

namespace Drupal\system\Access;

use Drupal\Core\Access\AccessResult;
use Drupal\Core\Routing\Access\AccessInterface;

/**
 * Access check for cron routes.
 */
class CronAccessCheck implements AccessInterface {
    
    /**
     * Checks access.
     *
     * @param string $key
     *   The cron key.
     *
     * @return \Drupal\Core\Access\AccessResultInterface
     *   The access result.
     */
    public function access($key) {
        if ($key != \Drupal::state()->get('system.cron_key')) {
            \Drupal::logger('cron')->notice('Cron could not run because an invalid key was used.');
            return AccessResult::forbidden()->setCacheMaxAge(0);
        }
        elseif (\Drupal::state()->get('system.maintenance_mode')) {
            \Drupal::logger('cron')->notice('Cron could not run because the site is in maintenance mode.');
            return AccessResult::forbidden()->setCacheMaxAge(0);
        }
        return AccessResult::allowed()->setCacheMaxAge(0);
    }

}