What is the main purpose of JSON Web Token (JWT) and how is it used?

JSON Web Token (JWT) is used for securely transmitting information between parties as a JSON object. The main purpose of JWT is user authentication and authorization in web applications. JWT contains an encoded payload with user data and is signed with a secret key or a pair of keys, allowing the authenticity of the token to be verified without the need to store state on the server.

Example of usage: after a user successfully logs in, the server issues a JWT, which the client sends in the headers of subsequent requests to confirm their identity.