17-webhook-security

My SDK verifies webhooks two different ways. Most SDKs only do one.

The eupago gateway offers two webhook formats: HMAC-SHA256 signed cleartext, and AES-256-CBC encrypted bodies. They're not "one or the other" — different merchants use different setups, and you only know which you'll receive when it lands.

In eupago-python both are first-class:

→ For HMAC signed webhooks: signature verification with constant-time compare. Not == on hex strings (that leaks timing). hmac.compare_digest, which is what hmac exists for.
→ For AES encrypted webhooks: derive the AES key from the webhook secret (SHA-256), pull the IV from the X-Initialization-Vector header, decrypt with PKCS7 padding. Then verify amount and currency match what you stored when you created the payment — signature valid is not business valid.
→ For both: dedup on a stable hash of the raw body so a re-delivery becomes a no-op.

"Just verify HMAC" is the README example everywhere. Production has more shapes.

If your webhook handler does == on hex strings, swap it for hmac.compare_digest before lunch. Easiest security win you can buy.

What's the security check your codebase ships without?

Repo: github.com/bilouro/eupago-python · Security docs: eupago.bilouro.com/security

P.S. New tech post every Wednesday.

#OpenSource #Python #SoftwareArchitecture