If you've ever built a web API, you've probably asked yourself: "How do I make sure only the right people can access certain routes?" That's exactly what authentication middleware solves — and in this guide, you'll learn how to do it in Axum 0.8 using JSON Web Tokens (JWT) . By the end of this article, you'll understand: What JWTs are and why they're useful How middleware works in Axum 0.8 How to write a JWT auth middleware from scratch How to protect routes and pass user data to your handlers Let's get started. What is a JWT? A JSON Web Token (JWT) is a compact, self-contained string that carries information about a user. It looks like this: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0IiwiZXhwIjoxNzAwMDAwfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c Enter fullscreen mode Exit fullscreen mode It has three parts separated by dots: Header — the algorithm used to sign the token (e.g. HS256 ) Payload — the actual data (e.g.…