The authorize action is used for authorizing off-session payments where the order is *already complete* and the order cycle may have closed (backoffice and subscriptions). They are essentially asynchronous and not coupled to the current open/closed state of the order cycle.
This Stripe-payment-authorizing logic is used by backoffice and subscriptions orders (but not the checkout), and was previously being handled by the #show action in Spree::OrdersController. It involves the user being redirected back to OFN after visiting a Stripe URL.