如何在使用支付网关时确认付款是否成功？

Question

This is how payment gateways works as I understand.

1. We send necessary POST Request to Payment Gateway (2checkouts, Paypal, etc).

2. Payments handle by Payments Getaway.

3. Then Payment Getaway send us POST parameters . Assume that Payment Getaway return parameters to example.com/return.php page.

I know that they send POST parameter like status or something. We can take it to verify the Payments.

So what we do is, we write a codes in example.com/return.php page to verify the payment.

But what happen if any user/hacker send all POST parameters (I mean as Payment Gateway send) to example.com/return.php page.

How should I handle about this?

Answer 1

You are supposed to verify that you get your POST parameters from the source you expect it to come from. In the case of Paypal, let's use their Instant Payment Notification (or IPN) as an example.

Looking at their IPN docs, they suggest:

Check email address to make sure that this is not a spoof

However, more importantly, you should look at:

verify_sign = AtkOfCXbDm2hu0ZELryHFjY-Vb7PAUvS6nMXgysbElEn9v-1XcmSoGtf

Before you can trust the contents of the message, you must first verify that the message came from PayPal. To verify the message, you must send back the contents in the exact order they were received and precede it with the command _notify-validate, as follows:

This means that, when you receive an IPN to example.com/return.php page, which can be at any time and not in the normal flow of a HTTP request / response that your end-user will be triggering, you then send this information back to PayPal and get them to verify that what you received was both correct and from them.

PayPal will then send one single-word message, either VERIFIED, if the message is valid, or INVALID if the messages is not valid.

So in your hypothetical example of someone sending spoofed data to your endpoint, PayPal would verify it as invalid anyway, and then you can go about what you need to do to make sure it doesn't happen again (logging, IPTables etc).