JWT in .NET — Your VIP Pass to the API World

JWT, one of the most important jargon in .NET, one of the most popular question in interview, so today let us understand what is JWT and how it works! Imagine you’re trying to get into an exclusive club — let’s call it “The .NET Lounge.” At the entrance, there’s a serious-looking bouncer (your API) who asks for your username and password. You tell him, he checks the list, and lets you in. All good, right? But here’s the problem: every time you step out to grab something from your car or visit the restroom, you have to stand in line and go through the whole ID check again. Annoying. This is exactly how old-school session-based authentication works — the server has to “remember” who you are every single time.

Now imagine a better system. The first time you enter, the bouncer hands you a shiny VIP pass — this is your JWT (JSON Web Token). It has three parts: a header (which says what kind of pass it is and how it’s signed), a payload (which contains your details like username, role, and expiry time), and a signature (the secret stamp that proves it’s authentic). You carry this pass around, and every time you return to the club, you just flash it at the bouncer. No list-checking, no repeated introductions. The bouncer just verifies the stamp and expiry date — if it’s valid, you’re in.

That’s exactly how JWT works in .NET. When you log in, your API verifies your credentials and generates a JWT using a secret key. You store this token on the client side (like in localStorage or sessionStorage). For every request after that, you include the token in the HTTP header as:

Authorization: Bearer <your-token>

Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWUsImlhdCI6MTUxNjIzOTAyMn0.KMUFsIDTnFmyG3nMiGM6H9FNFUROf3wh7SmqJp-QV30

The server’s authentication middleware checks the token’s signature and expiration time. If it’s genuine and still valid, you get access. If not — sorry, you’re out until you log in again. The beauty of JWT is that it’s stateless — the server doesn’t keep a session for every user. It works perfectly for distributed APIs, microservices, and even mobile apps. But like any VIP pass, it comes with responsibility: if someone steals your token, they can use it until it expires. That’s why it’s important to keep your JWT safe and set reasonable expiry times.In short, JWT in .NET is like a digital VIP pass that proves who you are without making the server remember you each time. It’s fast, lightweight, and secure (if implemented right) — just don’t lose it, or someone else might start enjoying your party!

Lets understand all of it using below image: