A JSON Web Token (JWT) is a compact, URL-safe way of representing claims that can be exchanged between parties.
All JWTs consist of a header and payload, which are JSON hashes. These objects are stringified and Base64-encoded. The encoded header and payload are combined with a digital signature (JWS), and all three components are concatenated with "." (period).
There are several reason to invalidate a JWT token before its expiration time: account deleted/blocked/suspended, password or permissions changed, user logged out by admin.
JWT is self-contained, signed and stored outside of the server context, so revoking a token is not a simple action.