RtlGetAce - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTRTL_H

NTSYSAPI
NTSTATUS
NTAPI
RtlGetAce(
    _In_ PACL Acl,
    _In_ ULONG AceIndex,
    _Outptr_ PVOID *Ace
    );

#endif

View code on GitHub

This function is documented in Windows Driver Kit.