Introduction
In modern web development, security is one of the most important aspects of building applications. Whether you are creating a web app, mobile app, or API, you need a secure way to authenticate users and protect data.
One of the most popular methods used today is JWT Authentication.
JWT (JSON Web Token) is widely used in modern web applications for secure authentication and authorization, especially in APIs, microservices, and cloud-based systems.
In this article, we will understand what JWT is, how it works, its structure, and why it is used in modern applications.
What is JWT (JSON Web Token)?
JWT stands for JSON Web Token. It is a compact, secure way of transmitting information between two parties as a JSON object.
JWT is a token that is used to verify the identity of a user after login.
Instead of storing session data on the server, JWT stores user information inside the token itself.
Real-Life Example
When you log in to an application:
Server generates a token
That token is sent to your browser
Your browser sends the token with every request
This is how JWT authentication works.
Structure of JWT Token
A JWT token has three parts:
Header.Payload.Signature
1. Header
Contains information about the token type and algorithm.
Example:
{
"alg": "HS256",
"typ": "JWT"
}
2. Payload
Contains user data and claims.
Example:
{
"userId": 101,
"email": "[email protected]"
}
3. Signature
Used to verify that the token is not modified.
It is created using:
Header
Payload
Secret key
How JWT Authentication Works (Step-by-Step)
Step 1: User Login
User enters username and password.
Step 2: Server Validates User
Server checks credentials in database.
Step 3: Token Generation
If valid, server creates a JWT token.
Step 4: Token Sent to Client
Token is sent to browser or app.
Step 5: Store Token
Client stores token in:
LocalStorage or
Cookies
Step 6: Send Token with Requests
Client sends token in headers:
Authorization: Bearer <token>
Step 7: Server Verifies Token
Server checks token validity and allows access.
Why JWT is Used in Modern Applications
1. Stateless Authentication
No need to store session on server.
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