Webhook Security Implementation Guide

Overview

This document provides a comprehensive guide to implementing secure webhook handling in Shipkit, with specific focus on Lemon Squeezy integration and payment processing webhooks.

🚨 Critical Security Requirements

1. Signature Verification

• ALWAYS verify webhook signatures using timing-safe comparison
• Never accept webhooks without proper signature validation
• Use environment variables for webhook secrets (LEMONSQUEEZY_WEBHOOK_SECRET)

2. Idempotency

• Store processed webhook event IDs to prevent duplicate processing
• Use database transactions for atomic operations
• Handle race conditions with proper locking mechanisms

3. Error Handling

• Return proper HTTP status codes (200 for success, 4xx for client errors)
• Never expose internal error details in webhook responses
• Implement comprehensive logging (excluding sensitive data)

Implementation Files

Core Implementation

• src/app/(app)/webhooks/lemonsqueezy/route.ts - Main webhook handler
• docs/integrations/security/LEMONSQUEEZY_WEBHOOK_SECURITY_AUDIT.md - Security audit checklist
• docs/integrations/lemonsqueezy-webhooks-best-practices.md - Comprehensive guide

Configuration

• src/env.ts - Environment variable validation
• Environment variables required:
  • LEMONSQUEEZY_WEBHOOK_SECRET - For signature verification
  • DATABASE_URL - For webhook event storage
  • LEMONSQUEEZY_API_KEY - For API operations

Best Practices Documentation

Rule Files (in .cursor/rules/)

• webhook-security.mdc - Comprehensive webhook security practices
• payments.mdc - Payment processing best practices
• security.mdc - Updated with webhook security sections
• error-handling.mdc - Updated with webhook error handling
• database.mdc - Updated with webhook data patterns

Quick Security Checklist

✅ Webhook signature verification implemented with timing-safe comparison ✅ Environment variables properly configured and validated ✅ Idempotency implemented using unique event identifiers ✅ Database transactions used for atomic operations ✅ Comprehensive error handling with proper HTTP status codes ✅ Sensitive data excluded from logs ✅ Rate limiting implemented ✅ Monitoring and alerting configured

Testing

• Test webhook endpoints in Lemon Squeezy sandbox environment
• Verify signature validation with invalid signatures
• Test idempotency with duplicate events
• Test error handling scenarios

Monitoring

• Track webhook success/failure rates
• Monitor processing times
• Set up alerts for webhook failures
• Regular security audits

Compliance

• PCI DSS compliance for payment webhooks
• GDPR compliance for customer data processing
• Regular security assessments

Support Documentation

• Lemon Squeezy Webhook Documentation