Handling JWT Authentications Securely: Pitfalls and Best Practices

When developing modern web applications, one of the most common authentication methods is using JSON Web Tokens (JWT). JWTs are powerful, but if not implemented securely, they can expose your application to various risks. In this blog, I’ll break down the common pitfalls developers face (PS: I faced them too..) with JWT and the best practices to ensure security across your application.

What is JWT?

JWT is an open standard (RFC 7519) that defines a way to securely transmit information between two parties as a JSON object. It's most commonly used for authentication in stateless systems.

A JWT consists of three parts:

1. Header: Contains the type of token (JWT) and the signing algorithm.
2. Payload: Contains the claims, such as user information, roles, and token expiration.
3. Signature: Used to verify the integrity of the token.

Go ahead and check out www.jwt.io

Common JWT Pitfalls

Despite its simplicity and power, improper JWT implementations can lead to significant security vulnerabilities, here are some common pitfalls I fall into & ways to improve.

Storing JWT in Local Storage

Pitfall: Many developers store JWTs in local storage due to its simplicity, but this approach is vulnerable to XSS (Cross-Site Scripting) attacks i.e. Hackers could easily steal that token through your browser and could pose as an authentic user.

Solution: Instead of local storage, store JWTs in HTTP-only cookies. These cookies are inaccessible to JavaScript, making lives of hackers a little bit more difficult.

No Token Expiry

Pitfall: If JWTs are created without an expiration time, they can be used indefinitely, even after the user logs out or if a token is compromised.

Solution: Always set an expiration (exp) claim in the payload. A reasonable expiry time forces users to refresh tokens regularly, reducing the window for potential token misuse.

Example

var token = jwt.sign({email_id:'123@gmail.com'}, "Stack", {
   expiresIn: '3d' // expires in 3 days
});

Exposing Sensitive Information in the Payload

Pitfall: This is a very common mistake I still tend to forget about, JWT payloads are base64-encoded but not encrypted, sensitive information (like passwords or secret keys) stored in the payload can be easily read by anyone without even a key!

Solution: Allways only store non-sensitive, non-critical information in the JWT payload, such as user roles or IDs. If you need to send sensitive data, encrypt the entire token payload.

Improper Token Revocation

Pitfall: JWTs are stateless by nature, so revoking tokens (e.g. after logout) can be tricky. Since there is no default way to handle this, we would need a custom solution for it. Without proper revocation, a JWT remains valid until it expires, allowing multiple JWTs per user active at a single time.

Solution: Implement a token blacklist or use refresh tokens. Store the token in a blacklist upon logout, and ensure the server checks the blacklist for each request. Alternatively, use short-lived access tokens combined with refresh tokens to force re-authentication more frequently.

Learnings

JWTs are an excellent tool for stateless authentication, but they need to be handled carefully to avoid introducing security risks. By avoiding common pitfalls and following best coding practices, I have learnt to create secure authentication systems and faced all these problems as a beginner.

Taking these steps will not only improve the security of your applications but also demonstrate your deep understanding of secure token management—a highly sought-after skill in the development world.