How JWT Authentication Works

A JSON Web Token (JWT) is a compact, URL-safe token that represents claims between two parties. It is composed of three parts:

• Header: Contains the type of token (JWT) and the signing algorithm being used (e.g., HMAC SHA256).
• Payload: Contains the claims. This is the part of the token where you can store user data and any other relevant information. Common claims include user ID, username, and roles.
• Signature: Used to verify the token's authenticity. It is created by encoding the header and payload, and then signing them using a secret key or a public/private key pair.

Structure of a JWT

A typical JWT looks like this:

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VybmFtZSI6ImpvaG5kb2UiLCJpYXQiOjE1MTYyMzkwMjJ9.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

This string consists of the header, payload, and signature separated by dots.

How JWT Authentication Works

JWT authentication typically follows these steps:

• Client Login: The client sends a login request with their credentials (e.g., username and password) to the server.

POST /login
{
  "username": "johndoe",
  "password": "password123"
}

• Server Validation: The server verifies the credentials. If valid, it creates a JWT containing the user's information and other claims.

• Token Generation: The server signs the JWT using a secret key and sends it back to the client.

{
  "token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..."
}

• Client Storage: The client stores the JWT, typically in local storage or cookies, for use in subsequent requests.

• Authenticated Requests: For future requests, the client includes the JWT in the HTTP headers.

GET /protected
Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...

• Server Verification: The server verifies the JWT’s signature and extracts the claims. If valid, it processes the request; if not, it responds with an error.

Benefits of JWT Authentication

• Stateless: JWTs are self-contained, meaning the server does not need to store session information, making it easier to scale applications.
• Security: JWTs can be signed and encrypted to ensure the integrity and confidentiality of the data they contain.
• Compact: The compact nature of JWTs makes them easy to pass in URL parameters, headers, or within the body of a POST request.
• Cross-Domain: JWTs are ideal for applications with multiple domains as they can be easily shared between them.