New CS proposal: [3rd Party Payment Gateway integration]

[mrojz]

What is the proposed Cheat Sheet about?

Guidance for securely integrating third-party payment gateways, focusing on workflow risks and practical mitigation steps.

What security issues are commonly encountered related to this area?

Order tampering, payment spoofing, unauthenticated callbacks, race conditions, replay attacks, and missing validation/logging.

What is the objective of the Cheat Sheet?

Enable fast, secure merchant integration by giving easy-to-follow technical checks for payment flows.

What other resources exist in this area?

https://owasp.org/www-project-web-security-testing-guide/latest/4-Web_Application_Security_Testing/10-Business_Logic_Testing/10-Test-Payment-Functionality

This Cheat Sheet is designed to guide developers to securly integrate 3rd party payment gateway integration.

• OWASP Web Security Testing Guide – Business Logic Testing
• Idempotency in Payment APIs – Stripe Docs
• 3rd Pary Payment Gateway API integration

[jmanico]

What a fantastic idea - this would be really useful to developers and seems quite practical.

[Prasad-JB]

This is a really valuable proposal. payment workflows are a common attack target, and a focused cheat sheet here would be very useful for developers.

Alongside the points already mentioned (order tampering, spoofing, replay, etc.), it might also be worth covering:

Idempotency & Replay Protection - ensuring transaction endpoints are idempotent, using nonces/tokens

Callback/Notification Validation - verifying signatures, mutual TLS, or HMAC on payment gateway callbacks

End-to-End Integrity - order amount + currency binding across the entire flow to prevent manipulation

Logging & Monitoring - capture anomalies like duplicate requests, mismatched amounts, or failed verifications

Secure Storage - ensure no sensitive cardholder/payment data is stored locally unless PCI-DSS compliant

I’d be happy to help draft the initial outline for the structure of the cheat sheet if we decide to move forward with this.