We felt that Checkout was the best integration point because it let us do some nice dynamic authentication logic instead of Alipay's usual redirect-based flow. Given that subtleties involved, Alipay's constraints, and the fact that it'll no doubt need to evolve in the future (as compared to the static standardization of credit cards), I think it'd be pretty tough to expose it via a straight API.
That makes sense. Given the fact Checkout simply returns a token, I think it's safe to say that it can still work with existing backend API solutions in conjunction with webhooks.
