If you've ever integrated a payment provider, GitHub Actions, or a third-party API that sends you events, you've used webhooks. And if you've ever worried about whether the request actually came from who it claims — or whether someone could forge one — you've run into the webhook security problem. The solution is HMAC verification. Here's how it works and how to implement it. The problem with unauthenticated webhooks Without verification, anyone who discovers your webhook endpoint URL can send requests pretending to be your payment processor or CI/CD system. Your server has no way to distinguish: A real payment notification from Stripe A fake request crafted by an attacker to trigger order fulfilment This is not theoretical. Webhook forgery has been used to trigger payouts, bypass authorization gates, and flood processing queues. HMAC: a shared secret approach HMAC (Hash-based Message Authentication Code) solves this with a shared secret.…