Secure Postbacks Explained (with HMAC Examples)

Why Secure Postbacks?

Postback security is essential to prevent fraud and ensure conversion data integrity. Without proper security, malicious actors could send fake postbacks to inflate conversion numbers or steal commissions.

HMAC (Hash-based Message Authentication Code) signatures provide a secure way to validate postbacks and ensure they come from legitimate sources.

How HMAC Validation Works

1. Merchant and affiliate share a secret key
2. Merchant creates HMAC signature using postback data and secret key
3. Merchant sends postback with signature
4. Affiliate server recalculates HMAC using same data and secret
5. Affiliate compares signatures - if they match, postback is valid

Implementation Best Practices

• Use strong, unique secret keys for each affiliate program
• Store secret keys securely (environment variables, secrets manager)
• Validate all postback parameters
• Implement timestamp validation to prevent replay attacks
• Log all postback attempts for auditing
• Return appropriate HTTP status codes