7 JWT Security Best Practices to Protect Apps Against Threats

JSON Web Tokens (JWTs) have revolutionized the way modern web applications handle user authentication, providing a lightweight, scalable solution. But with great power comes great responsibility, JWTs, if not implemented securely, can leave your application vulnerable to attacks such as token theft, tampering, and misuse. How do you safeguard JWTs from these threats? What are the best practices to ensure a robust and secure authentication system? 

In this blog, we’ll uncover the essential steps to protect your JWT-based authentication system, covering everything from secure token storage to implementing HTTPS and token rotation.

Why JWT Security Matters

JWTs are unique in that they are stored client-side, and this makes them particularly vulnerable to security risks. When tokens are improperly secured, attackers can steal, tamper, or misuse them to gain unauthorized access. To avoid these threats, let’s dive into essential best practices.

Best Practices for JWT Security

Here are the best practices for JWT Security:

Store JWTs Securely

Proper storage is key to JWT security. Storing tokens in a way that prevents unauthorized access is crucial:

• Use HTTP-Only Cookies: Store JWTs in HTTP-only cookies rather than localStorage or sessionStorage. HTTP-only cookies are not accessible via JavaScript, reducing the risk of token theft via cross-site scripting (XSS) attacks.

• Same-Site Attribute: Set the sameSite attribute to Strict to restrict cookies to the same domain, minimizing the risk of cross-site request forgery (CSRF).

Example:

res.cookie('token', token, {

  httpOnly: true,

  secure: true,  // Only send the cookie over HTTPS

  sameSite: 'Strict',  // Prevent CSRF attacks

});

Use HTTPS Everywhere

One of the simplest yet essential practices is to enforce HTTPS. This ensures that all data, including tokens, is encrypted during transmission. Without HTTPS, attackers could intercept and read tokens in plain text, a method known as a “man-in-the-middle” attack.

Tip: Set up HTTPS on both the server and client sides. Many cloud providers offer free SSL certificates to enable HTTPS.

Use Short Expiration Times for Access Tokens

Access tokens should be short-lived to limit the potential damage if they are compromised. For example, setting an access token to expire after 15 minutes reduces the attacker’s window of opportunity.

While short expiration times may seem inconvenient, this approach enhances security significantly. For a seamless user experience, pair short-lived access tokens with refresh tokens (covered in the next point) to allow re-authentication without requiring a login each time.

Implement Token Rotation for Refresh Tokens

Token rotation is a strategy where refresh tokens are rotated, or replaced, each time they’re used to request a new access token. By rotating tokens, you reduce the risk of replay attacks, where a stolen token is used repeatedly by an attacker.

To implement token rotation, use the following approach:

• Rotate the Refresh Token: Each time a refresh request is made, issue a new refresh token while invalidating the old one.

• Keep a Token Blacklist: Track invalidated tokens to prevent reuse by attackers in case of token theft.

Example of Token Rotation Flow:

• User Requests a New Access Token: The client sends a refresh token to the server.

• Server Verifies the Token: If valid, the server issues a new access token and refresh token, invalidating the old refresh token.

• Client Receives New Tokens: The client stores the new access and refresh tokens and uses the new access token for authentication.

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Validate Tokens Server-Side

Always validate JWTs server-side to ensure the token’s authenticity and integrity. Use your secret key or public key to verify tokens and ensure that they haven’t been tampered with. Avoid relying solely on client-side token validation, as this can be manipulated by an attacker.

Use Strong Secret Keys and Algorithms

When generating JWTs, always use a strong, complex secret key that attackers cannot guess. Avoid hardcoding secrets in your codebase, and consider using environment variables to manage them securely.

Also, use secure algorithms like HS256 or RS256 for signing JWTs. Avoid using weak algorithms that can be easily broken, compromising your tokens’ security.

Monitor and Log Authentication Events

Keeping a record of authentication activities can help detect suspicious behavior, such as frequent login attempts or repeated token refreshes. By monitoring these events, you can set up alerts for anomalies and take action quickly if unauthorized access is detected.

Example: Implementing Secure Token Storage in Express.js

To demonstrate how these best practices work in a real-world scenario, here’s how to securely store and handle tokens in an Express.js application.

const jwt = require('jsonwebtoken');
const SECRET_KEY = process.env.SECRET_KEY;


// Login Route - Setting secure HTTP-only cookie
app.post('/login', (req, res) => {
  const user = { username: req.body.username }; // Fetch or verify user
  const token = jwt.sign(user, SECRET_KEY, { expiresIn: '15m' });


  // Set secure, HTTP-only cookie for the token
  res.cookie('token', token, {
    httpOnly: true,
    secure: true,
    sameSite: 'Strict',
  });


  res.status(200).send('Login successful!');
});


// Middleware - Verifying JWT from HTTP-only cookie
function authenticateToken(req, res, next) {
  const token = req.cookies.token;
  if (!token) return res.sendStatus(403); // Forbidden if no token


  jwt.verify(token, SECRET_KEY, (err, user) => {
    if (err) return res.sendStatus(403);
    req.user = user;
    next();
  });
}

This code sample shows a secure approach to storing and authenticating JWTs in an Express.js application using HTTP-only cookies, protecting the tokens from direct JavaScript access.

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Wrapping Up

JWTs offer a flexible and efficient way to manage authentication, but their security hinges on proper implementation. By adopting best practices such as secure token storage, using HTTPS, enforcing short token lifespans, employing token rotation, and validating tokens server-side, you can significantly enhance the security of your authentication system.

Incorporating these measures not only defends your application against vulnerabilities like token theft and replay attacks but also ensures a smoother, safer user experience. Stay proactive, prioritize security, and your JWT-based system will remain resilient against evolving threats.

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