NetUserGetGroups

[DllImport("netapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
public static extern uint NetUserGetGroups(
   string ServerName,
   string UserName,
   uint Level,
   out IntPtr Buffer,
   uint PrefMaxLen,
   out uint EntriesRead,
   out uint TotalEntries
);

Microsoft documentation: Link