How to Implement HMAC Request Signing for Secure API Authentication in Node.js (2026 Guide)

HMAC request signing addresses the limitations of simple API keys by providing authentication, integrity verification, and replay protection through cryptographic signatures. The guide walks through building a complete Node.js implementation using Express middleware for server-side verification and a client SDK for signing requests, leveraging only the built-in Node.js crypto module. This pattern, used by AWS, Stripe, and Twilio, is increasingly critical in 2026 as AI agents and automated systems drive massive API traffic.