AJAX - JSON Web Tokens (JWT) with AJAX Authentication

JSON Web Token (JWT) is a secure method used to authenticate users between the client and the server. It is commonly used in modern web applications where AJAX requests communicate with backend services without reloading the page.

What is JWT

A JSON Web Token is a compact string that contains encoded user information. It is digitally signed by the server so that it cannot be modified by the client. Instead of storing session data on the server, authentication information is stored inside the token.

A JWT consists of three parts:

Header
Contains the token type and encryption algorithm.

Payload
Stores user data such as user ID, username, role, or permissions.

Signature
Ensures that the token is genuine and has not been changed.

These three parts are combined into a single string separated by dots.

How JWT Authentication Works with AJAX

1. User Login
   The user enters login credentials such as username and password.

2. AJAX Request Sent
   An AJAX POST request sends the login data to the server.

3. Server Verification
   The server validates the credentials. If they are correct, the server generates a JWT.

4. Token Sent to Client
   The server sends the JWT back to the browser.

5. Token Storage
   The client stores the token in localStorage, sessionStorage, or cookies.

6. Authenticated AJAX Requests
   Every future AJAX request includes the token in the Authorization header.

Example header:
Authorization: Bearer token_value

7. Server Validation
   The server checks the token before allowing access to protected resources.

Example Flow Using AJAX

Login request:
An AJAX request sends login details to the server.

Server response:
The server returns a JWT token.

Protected request:
AJAX includes the token while requesting secure data such as user profile or dashboard information.

Advantages of JWT with AJAX

Stateless authentication because the server does not need to store sessions.
Works well with single page applications.
Supports mobile apps and APIs easily.
Reduces server load compared to traditional sessions.

Security Best Practices

Always use HTTPS to protect tokens during transmission.
Avoid storing sensitive data inside the payload.
Set token expiration time.
Use refresh tokens for long sessions.
Protect against Cross-Site Scripting attacks when storing tokens.

Difference Between Session Authentication and JWT

In session authentication, the server stores user sessions.
In JWT authentication, the client stores the token and sends it with every request.

JWT combined with AJAX provides a fast, scalable, and modern authentication method widely used in REST APIs and single page applications.