MATTR Bundesdruckerei SPRIND This specification defines an extension to the OAuth 2.0 protocol (RFC 6749) that enables a client instance to include a key-bound attestation when interacting with an Authorization Server or Resource Server. This mechanism allows a client instance to prove its authenticity verified by a client attester without revealing its target audience to that attester. It may also serve as a mechanism for client authentication as per OAuth 2.0.