using System;
using System.Security;
using System.Security.Principal;
using System.Threading;
using System.Runtime.InteropServices;
using System.Text;

abstract class Win32Api
{
        [DllImport("Advapi32.dll")]
        public static extern bool LogonUser(
                string Username,
                string Domain,
                string Password,
                System.Int32 dwLogonType,
                System.Int32 dwLogonProvider,
                ref IntPtr phToken);
        
        [DllImport("Advapi32.dll")]
        public static extern bool GetTokenInformation(
                IntPtr TokenHandle,
                int TokenInformationClass,
                ref int TokenInformation,
                System.Int32 TokenInformationLength,
                ref System.Int32 ReturnLength);

        [DllImport("Kernel32.dll")]
        public static extern bool CloseHandle(
                IntPtr hObject);

        public const int LOGON32_LOGON_NETWORK=3;
        public const int LOGON32_PROVIDER_DEFAULT=0;
        public const int TOKEN_TYPE=8;
}

class Starter
{       
	public static void Main()
	{
                IntPtr pToken=IntPtr.Zero;
 
                bool resp=Win32Api.LogonUser("John", "", "test",
                        Win32Api.LOGON32_LOGON_NETWORK,
                        Win32Api.LOGON32_PROVIDER_DEFAULT,
                        ref pToken);
                if(resp==false)
                {
                        Console.WriteLine("Logon to user failed.");
                        return;
                }

                int nType=0, bytes=0;
                string prefix="";
                Win32Api.GetTokenInformation(pToken, Win32Api.TOKEN_TYPE,
                        ref nType, 4, ref bytes);
                if(nType==0)
                        prefix=" not";
                Console.WriteLine("John's token is {0} an impersonation token.",
                        prefix);
                WindowsIdentity newidentity=new WindowsIdentity(pToken);
                WindowsImpersonationContext wic=newidentity.Impersonate();
                       
                // Do something...
                Console.WriteLine("Doing something for John");

                wic.Undo();
                Win32Api.CloseHandle(pToken);

	}
}