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JWT: How Secure Are Your Tokens?

JWT: How Secure Are Your Tokens?

 By Charles Joseph | Cybersecurity Researcher
 Published on August 2nd, 2023
This post was updated on November 25th, 2023

JWT, which stands for JSON Web Token, is a compact, URL-safe means of representing claims to be transferred between two parties. It allows you to securely transmit information between parties as a JSON object, which is digitally signed to ensure its integrity. The encoded data can contain statements about an entity and some metadata. These tokens are designed to be compact, fast, and secure, and they are often used for single sign-on and information exchange scenarios.

How Secure Are JWT Tokens?

JSON Web Tokens (JWTs) can be very secure if implemented and managed correctly, but they’re not without potential vulnerabilities.

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A JWT includes a payload of data, which is digitally signed to ensure its authenticity and integrity. This digital signature means that if the data is tampered with, the token will be invalidated.

However, several potential vulnerabilities exist. If the token is intercepted, an attacker can read its contents because the information inside a JWT is encoded, not encrypted. Therefore, sensitive data should not be stored in a JWT unless it’s encrypted. Also, if the secret key used to sign the token is compromised, an attacker can forge tokens.

Furthermore, in some cases, an insecure configuration can enable an attacker to bypass the signature verification step entirely. Hence, while JWTs can be part of a secure system, they should be used appropriately, with additional safeguards such as HTTPS for transmission, limited token lifespan, secure storage of tokens on the client side, and rigorous key management practices.

JWT Examples

1. Authentication

Authentication is one of the most common utilizations of JWT. In practical terms, this typically begins when a user logs into a system. Upon successful login, the server creates a JWT and gives it back to the browser, which stores it for future use.

For every subsequent request from the user’s browser to the server, the JWT is included. This could be as a part of the header or as a URL parameter. The server receives this token and can easily verify it as the token is digitally signed. Once verified, the server trusts the token and knows the request has come from an authenticated user.

This process eliminates the need for the server to keep track of individual sessions, improving performance and scalability while still providing a reliable method to authenticate users. This methodology is particularly valuable in single-page applications, where it’s essential to manage user sessions without constant back-and-forth communication with the server.

2. Secure data exchange

In certain situations, two systems need to share information with each other in a secure manner. This is another scenario where JWTs demonstrate their usefulness. Let’s consider System A and System B as our examples.

System A first creates a JWT, placing the necessary data within it. The token is signed digitally to ensure its integrity and authenticity. This token, containing the relevant data securely inside it, is then sent over to System B.

Upon receipt, System B can easily validate the authenticity of the token due to the digital signature. Once validated, System B can trust the token information, knowing it originates from System A. It then extracts the data from the token. This process allows System A and System B to exchange information securely and efficiently.

3. Microservices

In a microservices architecture, applications are designed as independent and loosely coupled services. Each of these services ideally should be stateless to ensure scalability and ease of deployment. JWTs play an instrumental role in such architectures to help maintain user identity across these multiple microservices.

Once a user is authenticated via the first microservice, a JWT is generated and sent back to the user. Now, whenever the user makes a request to any of the other microservices, the JWT is sent along as well. Each of these microservices can then independently verify the token and ensure that the request is coming from an authenticated user.

As no session data needs to be stored with the service, it simplifies the process and increases performance. It also maintains consistency across the services as the user identity information is embedded within the JWT, reducing the need for data synchronization between different services.


In essence, JWT is a robust tool used in various scenarios such as authentication, secure data exchange, and maintaining user identity across microservices. It’s a secure, reliable, and efficient method of transmitting information, eliminating the need for session-based management and enhancing the overall performance of digital systems.

Key Takeaways

  • JWT stands for JSON Web Tokens, which are compact and URL-safe methods of transferring claims between two parties.
  • JWTs have several practical uses, including user authentication, secure data exchange, and maintaining user identity in microservices architecture without storing session data.
  • Each JWT is digitally signed, ensuring its integrity and trustworthiness. This signature allows for the verification of the sender and the data it contains.
  • JWTs are particularly useful in single-page applications, as they efficiently manage user sessions without requiring constant server communication.
  • Through JWTs, different systems or microservices can securely retrieve and verify user identity information, enhancing interoperability and performance.

Related Questions

1. How secure are JSON Web Tokens?

JWTs are quite secure, as they are digitally signed. This process ensures the identity of the sender and the integrity of the data. However, the contents of a JWT are not encrypted, so sensitive data should not be stored in them unless combined with other encryption methods.

2. What kind of data can be stored in a JWT?

JWTs can store any type of data that can be encoded as JSON. This data could include the user ID, token issuance time, token expiration time, or any other custom claims as needed by the application.

3. What is the structure of a JSON Web Token?

A JWT typically consists of three parts – the Header, the Payload, and the Signature. These sections contain the necessary information about the token type, encoded user-related data, and digital validation respectively.

4. Is JWT suitable for a mobile app authentication process?

Absolutely, JWTs are platform-independent and can be used for user authentication in mobile applications. Since they offer a stateless, server-side solution, they can provide secure, scalable user management across various platforms, including mobile.

5. What happens when a JWT expires?

Once a JWT expires, it can no longer be used for authentication or information exchange. The server will reject expired tokens, and a new token will need to be issued for continuing user sessions or data transfers.

"Amateurs hack systems, professionals hack people."
-- Bruce Schneier, a renown computer security professional
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