http://www.rfc-editor.org/rfc/rfc7800.txt
RFC 7800: Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs), M. Jones, J. Bradley, H. Tschofenig2016-04-01T23:00:00-00:00This specification describes how to declare in a JSON Web Token (JWT) that the presenter of the JWT possesses a particular proof-of- possession key and how the recipient can cryptographically confirm proof of possession of the key by the presenter. Being able to prove possession of a key is also sometimes described as the presenter being a holder-of-key.