What is a JWT?

A JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted.

Structure of a JWT

A JWT is composed of three parts, separated by dots ('.'):

• Header: Contains metadata about the token, such as the type of token and the signing algorithm used.
• Payload: Contains the claims, which are statements about an entity (typically, the user) and additional data.
• Signature: Used to verify that the sender of the JWT is who it says it is and to ensure that the message wasn't changed along the way.

Common Use Cases for JWTs

• Authentication: After a user logs in, a JWT can be returned and stored in the client, allowing the user to authenticate subsequent requests.
• Information Exchange: JWTs can be used to securely transmit information between parties, as the claims can be verified and trusted.
• Single Sign-On (SSO): JWTs can facilitate SSO, allowing users to log in once and access multiple applications without needing to log in again.