DbUpdateAccessCheck.php

<?php

namespace Drupal\system\Access;

use Drupal\Core\Routing\Access\AccessInterface;
use Drupal\Core\Access\AccessResult;
use Drupal\Core\Session\AccountInterface;
use Drupal\Core\Site\Settings;

/**
 * Access check for database update routes.
 */
class DbUpdateAccessCheck implements AccessInterface {
    
    /**
     * Checks access for update routes.
     *
     * @param \Drupal\Core\Session\AccountInterface $account
     *   The currently logged in account.
     *
     * @return \Drupal\Core\Access\AccessResultInterface
     *   The access result.
     */
    public function access(AccountInterface $account) {
        // Allow the global variable in settings.php to override the access check.
        if (Settings::get('update_free_access')) {
            return AccessResult::allowed()->setCacheMaxAge(0);
        }
        if ($account->hasPermission('administer software updates')) {
            return AccessResult::allowed()->cachePerPermissions();
        }
        else {
            return AccessResult::forbidden()->cachePerPermissions();
        }
    }

}