OAuth 2.0 Proof-of-Possession: Authorization Server to Client Key Distribution

RFC 6750 specified the bearer token concept for securing access to protected resources. Bearer tokens need to be protected in transit as well as at rest. When a client requests access to a protected resource it hands-over the bearer token to the resource server. The OAuth 2.0 Proof-of-Possession security concept extends bearer token security and requires the client to demonstrate possession of a key when accessing a protected resource.