The .NET Developer's Guide to Windows Security

Chapter 26. How to Get a Token for a User

Getting a token (Item 16) for a user is tremendously easy if you happen to be running on a Windows Server 2003 machine in a native Windows Server 2003 domain. You can simply construct a new Windows Identity, passing in the user principal name (UPN) for the account, which for ACME\Alice is typically something like [e-mail].^[1] Here's an example:

using System;
using System.Security.Principal;

class IsUserAnAdmin {
  static void Main(string[] args) {
    if (1 != args.Length) {
      Console.WriteLine("Usage: IsUserAnAdmin userPrincipalName");
      return;
    }
    string upn = args[0];
    // here's the magic constructor
    WindowsIdentity id = new WindowsIdentity(upn);
    WindowsPrincipal p = new WindowsPrincipal(id);
 if (p.IsInRole(WindowsBuiltInRole.Administrator)) ...