Siemens AG Siemens AG Atos Research and Innovation This specification defines PAT, "Privacy-Enhanced-Authorization- Tokens", an efficient protocol and an unlinkable-token construction procedure for client authorization in a constrained environment. This memo also specifies a profile for ACE framework for Authentication and Authorization. The PAT draft uses symmetric cryptography, proof-of-possession (PoP) for a key owned by the client that is bound to an OAuth 2.0 access-token.