This document details the Microsoft authorization data present in Kerberos tickets issued by Windows domain controllers. Kerberos is an authentication and key distribution protocol; its primary purpose is to authenticate two principals to each other, and establish a cryptographic key that the two can use to secure any messages. However, there is a provision in the ticket for vendor supplied authorization data. Microsoft uses that field to convey the group membership information for the user identified in the ticket. For anyone writing to the Windows platform, this is all handled by the operating system; the group information is extracted from the ticket by the kerberos security package, and used to create a token (c.f. Access token) that can be used by the server for access checks (c.f. ImpersonateSecurityContext, RpcImpersonateClient, AccessCheck, and so on).
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