Harden ITN handling: validate paid amount and dedupe repeated notifications#16
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Two defects in onNotify()/processOrder() that affect payment integrity: 1. Amount tampering. The ITN signature is verified, but the gross amount originates from the process-page POST the buyer controls. The handler recorded amount_gross verbatim without comparing it to the order total, so a completed payment could be booked for less than the cart value. Now the paid gross is compared to $order->getTotalPrice() (ZAR, 0.01 tolerance) and mismatches are logged and rejected. 2. Duplicate payments. Payfast re-sends the ITN until it receives a 200, so each retry created another completed payment for the same pf_payment_id. processOrder() now short-circuits when a payment with that remote_id already exists. loadPaymentByRemoteId() is corrected to query remote_id (the Payfast transaction id) instead of order_id, which every payment on the order shares, and to bail out safely if the payment storage cannot load.
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Two payment-integrity defects in `onNotify()` / `processOrder()`, independent of #12.
1. Amount tampering (security)
The ITN signature is verified, but `amount_gross` originates from the process-page POST the buyer controls. The handler recorded it verbatim, so a completed payment could be booked for less than the cart total. The paid gross is now compared to `$order->getTotalPrice()` (ZAR, 0.01 tolerance); mismatches are logged and rejected. This mirrors the amount check in PayFast's own ITN integration guidance.
2. Duplicate payments (idempotency)
PayFast re-sends the ITN until it receives a 200, so each retry created another
completedpayment for the samepf_payment_id.processOrder()now returns early when a payment with thatremote_idalready exists.Supporting fix
loadPaymentByRemoteId()queriedorder_id(shared by every payment on the order) despite its name; it now queriesremote_id(the PayFast transaction id) and returnsFALSEsafely if payment storage cannot load.Scope: one file,
OffsiteRedirect.php. No behaviour change for correctly-formed single ITNs.