JWT能够干什么，不应该干什么？

http://cryto.net/~joepie91/blog/2016/06/13/stop-using-jwt-for-sessions/

At the start of this article, I said that there are good usecases for JWT, but that they're just not suitable as a session mechanism. This still holds true; the usecases where JWT is particularly effective are typically usecases where they are used as a single-use authorization token.

From the JSON Web Token specification:

JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. [...] enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted.

In this context, "claim" can be something like a 'command', a one-time authorization, or basically any other scenario that you can word as:

Hello Server B, Server A told me that I could <claim goes here>, and here's the (cryptographic) proof.

For example, you might run a file-hosting service where the user has to authenticate to download their files, but the files themselves are served by a separate, stateless "download server". In this case, you might want to have your application server (Server A) issue single-use "download tokens", that the client can then use to download the file from a download server (Server B).

When using JWT in this manner, there are a few specific properties:

• The tokens are short-lived. They only need to be valid for a few minutes, to allow a client to initiate the download.
• The token is only expected to be used once. The application server would issue a new token for every download, so any one token is just used to request a file once, and then thrown away. There's no persistent state, at all.
• The application server still uses sessions. It's just the download server that uses tokens to authorize individual downloads, because it doesn't need persistent state.

As you can see here, it's completely reasonable to combine sessions and JWT tokens - they each have their own purpose, and sometimes you need both. Just don't use JWT for persistent, long-lived data.