Managing JWT Expiration and Refresh

1. Introduction

In modern web applications, JWT (JSON Web Tokens) are frequently used for authentication. Managing the expiration of JWTs and implementing a refresh mechanism is crucial for maintaining security and a seamless user experience.

2. JWT Overview

JWT is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure.

A typical JWT consists of three parts:

• Header
• Payload
• Signature

3. JWT Expiration

JWTs often include an expiration claim (`exp`) that specifies the time after which the token is no longer valid. This is important for security as it limits the time frame in which a stolen token can be used.

4. Refresh Tokens

To enhance user experience while maintaining security, refresh tokens are used. A refresh token allows the application to obtain a new access token without requiring the user to log in again.

Typically, refresh tokens have a longer expiration time than access tokens. When an access token expires, the application can use the refresh token to request a new access token from the server.

5. Implementation

Here’s a step-by-step guide to implementing JWT expiration and refresh in a front-end application:

Step 1: Obtain JWT and Refresh Token

        // Sample API call to authenticate and receive tokens
        async function login(username, password) {
            const response = await fetch('/api/login', {
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json'
                },
                body: JSON.stringify({ username, password })
            });
            const data = await response.json();
            if (response.ok) {
                localStorage.setItem('accessToken', data.accessToken);
                localStorage.setItem('refreshToken', data.refreshToken);
            }
        }
        

Step 2: Use Access Token

        // Function to make an authenticated API request
        async function fetchData() {
            const token = localStorage.getItem('accessToken');
            const response = await fetch('/api/data', {
                method: 'GET',
                headers: {
                    'Authorization': `Bearer ${token}`
                }
            });
            return response.json();
        }
        

Step 3: Handle Token Expiration

        // Check for token expiration
        function isTokenExpired(token) {
            const payload = JSON.parse(atob(token.split('.')[1]));
            return payload.exp * 1000 < Date.now();
        }
        

Step 4: Refresh Access Token

        // Function to refresh the access token
        async function refreshAccessToken() {
            const refreshToken = localStorage.getItem('refreshToken');
            const response = await fetch('/api/refresh', {
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json'
                },
                body: JSON.stringify({ refreshToken })
            });
            const data = await response.json();
            if (response.ok) {
                localStorage.setItem('accessToken', data.accessToken);
            }
        }
        

6. Best Practices

• Always use HTTPS to prevent token interception.
• Set short expiration times for access tokens.
• Implement secure storage for refresh tokens, such as HttpOnly cookies.
• Regularly rotate refresh tokens to enhance security.
• Log out users and invalidate tokens when necessary.

7. FAQ