JWT from A to Z: A Modern Authentication Solution for Developers

By Ashiq

 

JWT from A to Z: A Modern Authentication Solution for Developers

In the world of software engineering, it's rare to find someone who hasn't heard of JSON Web Token (JWT) when dealing with authentication and authorization. However, even when we use it, we often remain somewhat unclear about its internal workings and security aspects. In this article, we will explore JWT from a new perspective—from its structure to its necessity in modern systems and best security practices.



1. What is JWT and Why is it Used?

JSON Web Token (JWT) is an open standard (RFC 7519) primarily used as a secure means of transmitting information between two parties. It is highly popular in modern distributed systems and microservice architectures because it is Stateless. This means the server does not need to store user session data in a database; the token itself carries its own identity.


2. Dissecting the Token: The Internal Structure of JWT

Generally, a JWT token is composed of three parts: header, payload, and signature. These parts are separated from each other by dots (.), and each part is encoded using Base64 URL encoding. A JWT token typically appears in the format: header.payload.signature.

a. Header

This section contains information about the token type (JWT) and the algorithm used to sign it (e.g., HS256 or RS256).

b. Payload

This is the core part of the token, containing user information or Claims. For example: user ID, name, token issuance time (iat), expiration time (exp), and so on.

c. Signature

The signature is used to verify the integrity of the token—to ensure it hasn't been tampered with after being issued. It is created using the header, payload, and a secret key.


3. Security Reality Check: What You Need to Know

When using JWT, some misconceptions can increase our security risks:


  • Encoded, Not Encrypted: Remember, JWT does not encrypt data; it only encodes it. Anyone can decode the token and view the information in the payload. Therefore, never store sensitive information like passwords or secret keys in the Payload.

  • Integrity vs. Confidentiality: The purpose of the signature is to prevent data tampering or alteration, not to hide data.


4. Modern Implementation and Best Practices

To build a secure system, the following practices are mandatory:


  1. Use HTTPS: Always use an encrypted connection (HTTPS) to prevent token theft.

  2. Short-lived Tokens: Access tokens should always have a short expiration period (e.g., 15-30 minutes).

  3. Refresh Token Strategy: For prolonged login sessions, use refresh tokens and token rotation methods.

  4. Strong Algorithms: If possible, use RS256 (Asymmetric key-based), which is more secure than HS256.

  5. Blacklisting: If necessary, implement a blacklisting mechanism using a database or Redis to invalidate tokens.


5. Decision: When to Use JWT?

JWT is not a one-size-fits-all solution. Choose the right method based on your project's nature. Here are some key differences between Session-based Authentication and JWT:

Session-based Authentication:

  • Scalability: Storing session data on the server can make it difficult to scale, especially when multiple servers are used.

  • Control: The server can invalidate or delete a session at any time, immediately revoking user access.

  • Usage: It is generally suitable for traditional web applications.

JWT (Token-based) Authentication:

  • Scalability: JWT is Stateless, meaning no session data is stored on the server. This makes it highly scalable for microservices and distributed systems.

  • Control: Once issued, a token remains valid until its expiration. It is difficult for the server to revoke it immediately unless a blacklisting mechanism is used.

  • Usage: It is more suitable for mobile applications, Single-Page Applications (SPAs), and API-driven systems.


Conclusion

JWT is not a magical solution, but rather a powerful tool. Before using it, consider your system's security requirements and scalability. By adhering to proper best practices, JWT can make your application more dynamic and secure.


References and Further Reading:

  1. RFC 7519 - JSON Web Token (JWT)

  2. JWT.io - Introduction to JSON Web Tokens

  3. OWASP - JSON Web Token Cheat Sheet

  4. Auth0 - JWT Best Practices

  5. JSON Web Token (JWT) arguments

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