Unfortunately I can't share a demo or docs as this is NDA work we did for the client (and the commerce is still in alpha).
But basically you're right. We would create a new checkout page (for the link) that would show the items of the cart (through the Commerce Platform API) and with the credit card fields shown (that would be later sent to the gateway). The link is for the checkout, so you'd have only one per cart/client and it has a timed session.