I think the best way is to dispatch a new event in `SecurityStep` https://github.com/Sylius/Sylius/blob/master/src/Sylius/Bundle/CoreBundle/Checkout/Step/SecurityStep.php#L49
So that you can attach `$order` to the event dispatched (like all other checkout events). I don't know why there isn't already an event dispatched in this action (in addition to the FOSUB events that are not checkout specific).