The S4U2self extension allows a service to obtain a service ticket to itself on behalf of a user. The user is identified to the KDC using the user's name and realm. Alternatively, the user might be identified based on the user's certificate. The Kerberos ticket-granting service (TGS) exchange request and response messages, KRB_TGS_REQ and KRB_TGS_REP, are used along with one of two new data structures. The new PA-FOR-USER data structure is used when the user is identified to the KDC by the user name and realm name. The other structure, PA-S4U-X509-USER, is used when the user certificate is presented to the KDC to obtain the authorization information. By obtaining a service ticket to itself on behalf of the user, the service receives the user's authorization data in the ticket.