Payment cancellation

[ashitikov]

Is your feature request related to a problem? Please describe.
Current implementation of 'cancel' payment state is like a dummy. I can cancel payment from any state, so its gonna be a problem if payment is in 'authorized' or 'settled' state and I click cancel in admin-ui. Literally we may lose payments, without any callback to payment provider.

Describe the solution you'd like
A new payment handler's method 'cancelPayment' which carefully handle this type of transition. In two-step scheme we could cancel payment transaction, which will unblock held funds, instead invoking a refund.

Describe alternatives you've considered
Handle this type of action as refund, but I guess there is a lot of side effects on order.

@michaelbromley
Hi,
I think you are right - currently it's just setting state to Cancelled and no side effects are happening. It should not really be possible to just cancel a settled payment - you'd also want to take the corresponding action with the payment provider like with "refund".

So I think basically I added this state way back when I implemented Payments but before actually having implemented a concrete provider integration, hence this rather impractical functionality.

@ashitikov
It's quite helpful in case of two-step payment flow
Transition authorized -> cancelled is possible in this case. Corresponding method cancelPayment should be called in payment handler in this case

@michaelbromley
yes, then we'd need to add a cancelPayment method to the handler API.

Slack thread: https://vendure-ecommerce.slack.com/archives/CKYMF0ZTJ/p1656319311851299

[michaelbromley]

@martijnvdbrug, @vrosa - the above commits introduce a new optional function to PaymentMethodHandlers, cancelPayment(). This is designed to allow you to cancel a "started but not yet completed" payment, which e.g. in Stripe probably corresponds to a payment intent, and in Mollie probably corresponds to an open payment which can still be cancelled.

Just giving you guys the heads up so that you can potentially incorporate this API into your own implementations once v1.7 is out, and if it proves beneficial, perhaps contribute the changes back to the payments-plugin versions of Stripe and Mollie handlers.