Software Design

Secure Webhook Verification via HMAC Signatures

UML Sequence Diagrams · made in Skemio

Sequence diagram of Webhook Sender, Target API, and Secrets Store validating signature and checking against replay window.
Sequence diagram of Webhook Sender, Target API, and Secrets Store validating signature and checking against replay window.
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What it shows

  • Signatures must be computed over the raw HTTP request body string.
  • Compare signatures using constant-time algorithms to prevent timing attacks.
  • Validate embedded timestamps to prevent unauthorized replay attacks.

The takeaway

Always verify HMAC signatures with raw bytes and constant-time comparisons before processing webhooks.

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