Why Many Developers Advise Against Using JWT for Authentication?

JSON Web Tokens (JWT) have gained popularity for web application authentication due to their simplicity and stateless nature. They enable secure information exchange between two parties and are frequently used in login systems. However, despite their widespread use, many security experts and developers advise against using JWTs for session management.

In this article, we’ll explore why JWTs raise concerns and why many recommend alternative solutions.

What is JWT?

A JSON Web Token (JWT) is a compact, URL-safe token used to transmit claims between two parties. It is digitally signed to ensure that the data hasn’t been tampered with. A JWT consists of three main components:

• Header: Defines the signing algorithm.
• Payload: Contains claims (data).
• Signature: A hashed combination of the header and payload for data integrity.

JWTs are commonly used for authentication by issuing a token after a user logs in. The token is stored client-side and sent with subsequent requests. The server verifies the token without having to maintain session data. So why is this method discouraged by many?

1. JWT Size: A Hidden Cost

One of the major drawbacks of JWT is its size. Unlike session cookies, JWTs carry their own payload, which includes user information like IDs, roles, and metadata, making them significantly larger.

• A traditional session cookie storing just a user ID is very small.
• A JWT, in contrast, includes the user ID, metadata, and a digital signature, making it much larger.

This increased size can lead to higher bandwidth usage as the token is sent with every request, which can be especially problematic in low-bandwidth scenarios or on mobile devices.

2. Token Revocation: A Security Weakness

JWTs lack a simple method for revocation, which presents a significant security risk.

• The Logout Problem: In a traditional session system, logging out invalidates the session immediately. With JWTs, however, the server cannot directly invalidate the token without storing it server-side, which defeats the purpose of JWTs being stateless. If the token has a long expiration time, a stolen token could remain valid for an extended period, even after a user logs out.

• Stale Tokens: In a session-based system, when a user’s privileges change (e.g., an admin is demoted), the session on the server is updated instantly. With JWT, changes are only reflected once the token expires, which can leave users with outdated permissions.

3. Redundant Signatures

JWTs are praised for their tamper-evident digital signatures. However, modern web frameworks automatically sign session cookies, making the JWT signature redundant in many cases.

• If you’re using JWTs in a cookie, the framework often signs and encrypts the cookies automatically, meaning both the cookie and JWT have signatures, which adds unnecessary complexity.

In practice, traditional session cookies provide the same security level as JWTs but without the added size and complexity.

4. Security Vulnerabilities

JWTs are typically not encrypted, meaning that while the data is base64-encoded, it’s not hidden. Anyone intercepting the token can easily decode the payload.

• Man-in-the-Middle Attacks: If JWTs aren’t transmitted over HTTPS, attackers can intercept and access sensitive session information.
• Weak Signing Algorithms: In some cases, attackers have exploited weak JWT signing algorithms, allowing them to bypass security measures entirely through algorithm spoofing.

Always using HTTPS and strong signing algorithms helps mitigate these risks, but they can still pose issues.

5. Lack of Immediate Expiry Control

While JWTs include an expiration time (exp), this is managed client-side. A compromised token remains valid until it expires, allowing an attacker to use it for as long as it’s valid, regardless of whether it’s been compromised.

In contrast, session-based authentication allows for immediate session invalidation, providing much better control over active sessions.

6. Overcomplicating Simple Use Cases

In many cases, using JWTs is overkill. Traditional session-based authentication with cookies and server-stored session data can handle most authentication needs without the complexities of stateless JWTs.

For example, if your app simply needs to track logged-in users, a cookie-based solution is more efficient. Many modern web frameworks handle cookies, signing, and encryption for you, making JWT unnecessary in most scenarios.

Conclusion: When Not to Use JWT

JWTs can be valuable in specific use cases like API authorization or single-use tokens, but for session management in most web applications, traditional session cookies are often a better option. They are smaller, easier to manage, and offer better security for long-lived sessions.

Avoid JWTs if:

• You need immediate token revocation.
• You want to minimize bandwidth usage.
• You’re handling sensitive, long-lived sessions.

While JWTs offer a stateless and self-contained approach, they come with performance and security trade-offs. Before adopting JWTs, consider whether they are the right solution for your application’s needs.