Webhook Security Essentials: Preventing Signature Spoofing with HMAC-SHA256

Most webhook implementations have critical signature verification bugs—or skip verification entirely, creating exploitable security gaps. When handlers process payments, create accounts, or trigger workflows, unverified requests enable fraud and system compromise. This guide provides production-ready HMAC-SHA256 patterns for Node.js, Python, and Ruby, exposing the six subtle mistakes that break otherwise-correct code across Stripe, GitHub, Shopify, and other major platforms.