The WIN_TRUST_SIP_SUBJECT structure identifies the subject to be evaluated by a Subject Interface Package (SIP). A SIP is a third-party component of the WinTrust service that can evaluate a subject to verify its authenticity.
typedef struct _WIN_TRUST_SIP_SUBJECT {
    GUID *                  SubjectType;
    WIN_TRUST_SUBJECT       Subject;
} WIN_TRUST_SIP_SUBJECT, *LPWIN_TRUST_SIP_SUBJECT;
 
Each SIP supports a unique set of subject types that it can evaluate. For
information about specific subject types, see the documentation for the
individual SIPs. 
WinTrustSubjectCheckContentInfo, WinTrustSubjectEnumCertificates, WinTrustSubjectGetCertHeader, WinTrustSubjectGetCertificate, WinTrustSubjectGetName