Webhook Design Best Practices: Security, Retries, & Signatures
Design reliable outbound event notifications: HMAC-SHA256 signature verification, retry schedules with exponential backoff, manual replay, and developer logs.
01.What are Webhooks & The Outbound Engineering Hazards
A Webhook (sometimes called a Reverse API) is an event-driven mechanism where a server initiates an outbound HTTP POST request to a third-party developer's public URL whenever a domain event occurs (e.g., an invoice is paid, a GitHub pull request is merged, a shipment status changes).
The Hazards of Outbound Webhook Delivery:
- The Hanging Receiver Problem: A poorly written third-party client endpoint might execute slow database queries and hang for 60+ seconds without returning a response. Without strict timeouts, your outbound dispatch workers exhaust their thread/socket pools and crash.
- Third-Party Server Outages: Customer servers frequently go down for maintenance, reboot, or deploy breaking bugs. Your system must reliably buffer and retry events without losing data.
- Forged & Tampered Requests: Attackers can discover a merchant's webhook URL and send fake
"payment.succeeded"payloads to trick the merchant into fulfilling orders without paying. - Replay Attacks: An attacker intercepts a legitimate historical webhook payload and replays it to the customer's server to trigger duplicate side effects.
Secure Outbound Webhook Delivery & Retry Pipeline 🔐
Secure Outbound Webhook Delivery & Retry Pipeline 🔐
Cryptographic HMAC signature validation, strict HTTP timeouts, and exponential backoff retry scheduling.
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