JSON Web Tokens (JWTs) are still a pretty new standard for carrying out authentication; not everyone knows about them, and even fewer people use them. This section does not provide a theoretical excursion through the mathematical or cryptographic basics of JWTs.
In traditional web applications written in PHP, for example, you commonly have a session cookie. This cookie identifies the user session on the server. The session must be stored on the server to retrieve the initial user. The problem here is that the overhead of saving and querying all sessions for all users can be high. When using JWTs, however, there is no need for the server to preserve any kind of session id.
Generally speaking, a JWT consists of everything you need to identify a user. The most common approach is to store the creation time of the token, the username, the user id, and maybe the role...