NServiceBus.MessageQueueExtensions.GetAce C# (CSharp) Method

        static ACCESS_ALLOWED_ACE GetAce(IntPtr pDacl, string sid)
        {
            var AclSize = new ACL_SIZE_INFORMATION();
            GetAclInformation(pDacl, ref AclSize, (uint) Marshal.SizeOf(typeof(ACL_SIZE_INFORMATION)), ACL_INFORMATION_CLASS.AclSizeInformation);

            for (var i = 0; i < AclSize.AceCount; i++)
            {
                IntPtr pAce;
                GetAce(pDacl, i, out pAce);
                var ace = (ACCESS_ALLOWED_ACE) Marshal.PtrToStructure(pAce, typeof(ACCESS_ALLOWED_ACE));

                var iter = (IntPtr) ((long) pAce + (long) Marshal.OffsetOf(typeof(ACCESS_ALLOWED_ACE), "SidStart"));
                var size = GetLengthSid(iter);
                var bSID = new byte[size];
                Marshal.Copy(iter, bSID, 0, size);
                IntPtr ptrSid;
                ConvertSidToStringSid(bSID, out ptrSid);

                var strSID = Marshal.PtrToStringAuto(ptrSid);

                if (strSID == sid)
                {
                    return ace;
                }
            }

            throw new Exception($"No ACE for SID {sid} found in security descriptor");
        }
    }