What is JWT (JSON Web Token)?

1. Definition

JWT (JSON Web Token) is a secure way to transmit information between client and server as a JSON object. It is commonly used for authentication and authorization.

2. Structure of JWT

Header.Payload.Signature

Header: Algorithm & token type
Payload: User data (id, email)
Signature: Security verification

3. How it Works

User logs in with credentials
Server generates JWT
Token is sent to client
Client sends token in future requests
Server verifies token

4. Example

const jwt = require("jsonwebtoken");

const token = jwt.sign(
  { userId: 1 },
  "secretKey",
  { expiresIn: "1h" }
);

console.log(token);

5. Where JWT is Used

User authentication
Authorization (protected routes)
Secure API communication

6. Advantages

Stateless authentication
Compact and secure
Works across different platforms
Easy to implement