#ifndef _NTRTL_H
NTSYSAPI
NTSTATUS
NTAPI
RtlGetGroupSecurityDescriptor(
    _In_ PSECURITY_DESCRIPTOR SecurityDescriptor,
    _Outptr_result_maybenull_ PSID *Group,
    _Out_ PBOOLEAN GroupDefaulted
    );
View code on GitHubThis function is documented in Windows Driver Kit.