Nex Webhook Handler Pattern

The problem

Webhook handlers often fail due to slow processing timeouts, lack of idempotency, or incorrect signature verification. Developers frequently struggle with replay attacks and lose visibility into missed deliveries when workers crash.

What it does

• Generates provider-specific cryptographic signature verification for Stripe, Resend, Clerk, and others.
• Implements a verify-then-store-then-enqueue flow to ensure data integrity.
• Creates an audit table with a unique constraint on provider event IDs to prevent duplicate processing.
• Offloads heavy logic to ARQ background jobs, allowing the FastAPI handler to return a 200 OK within one second.
• Includes a replay CLI to re-run unprocessed or failed events from the audit log.

Frameworks & tools

FastAPI, ARQ (Redis-based task queue), PostgreSQL, and Pydantic.

Why this beats prompting it yourself

Signature verification contracts vary wildly between providers. This skill uses hard-coded, production-tested patterns for header parsing and timestamp tolerance that generic prompts often hallucinate or oversimplify, leaving you vulnerable to replay attacks.

Use cases

• Hardening a Stripe integration against signature-bypass and replay attacks.
• Recovering from worker outages by replaying missed events from an audit table.
• Standardizing webhook ingestion across multiple providers like Cloudflare and Postmark.
• Debugging "silent failures" where webhooks fire but no business logic executes.

Known limitations

Designed specifically for FastAPI and ARQ. Porting to Express or Next.js requires manual adaptation of the dependency injection and queueing logic.