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 JavaScript Object Notation (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 MACed and/or encrypted.
Specification: http://self-issued.info/docs/draft-ietf-oauth-json-web-token.html
Further Explanation: https://developer.atlassian.com/static/connect/docs/concepts/understanding-jwt.html
Several versions including for NodeJS