Can JWT implement dynamic permission changes? What is the difference from the Session mechanism?

JWT and Session: In-depth understanding and its application in dynamic permission control

JWT (JSON Web Token) and Session mechanisms are two commonly used authentication and authorization solutions. Beginners are often confused about their characteristics and applicable scenarios, especially in terms of dynamic permission changes (such as "kicking people" operations). This article will elaborate on this.

Some people believe that JWT is a way to persist user information to the browser, and the server needs to trust JWT information. This raises a key question: Can JWT implement dynamic permission changes? If not, does the server need to fall back to the Session mechanism?

The advantage of JWT is its efficiency: after receiving the request, the server directly extracts user information from the JWT without additional database queries. However, in dynamic permission change scenarios, this advantage no longer exists. The server still needs to query the database to verify the user's real-time permissions, and the information stored in the JWT may have expired. Instead of storing redundant user information in JWT, it is better to use only a small token as the identifier for the database query, which is more efficient.

Therefore, JWT is more suitable for inter-service communication. For example, after the gateway service verifies the user's identity, it generates a JWT and adds it to subsequent requests. The subsequent service directly uses JWT information, without having to access the user service again, and each request uses an independent JWT, avoiding the complexity of permission changes.

The Session mechanism can be understood as a key-value pair mapping: the client requests to carry a key (such as Session ID), and the server uses this key to find the corresponding Session information. Cookies are usually used to store Session IDs. In non-browser environments (such as Apps), tokens also play a role similar to Session ID. JWT actually converts "find Session" to "parse Session", which is essentially not separated from the core idea of ​​the Session mechanism.

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