A method for creating a proof of possession confirmation for inclusion by an attribute certificate authority into an attribute certificate, the attribute certificate for use by an end user. The method includes receiving from the attribute certificate authority in response to a request by the end user, a plurality of data fields corresponding to a target system, the identity of the end user, and a proof of identity possession by the end user. The method further includes preparing a data structure corresponding to an authorization attribute of the attribute certificate, the data structure including a target system name, the identity of the end user, and the key identifier of the end user. Using a private key associated with the target system, the method includes signing the data structure resulting in a proof of possession confirmation, and sending the proof of possession confirmation to the attribute certificate authority for inclusion into the attribute certificate.