using System;
using System.Runtime.InteropServices;
using System.Security.Principal;
using System.Security.Permissions;
using Microsoft.Win32.SafeHandles;
using System.Runtime.ConstrainedExecution;
using System.Security;

namespace FetchFile
{
    class Program
    {
        [DllImport("advapi32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
        public static extern bool LogonUser(String lpszUsername, String lpszDomain, String lpszPassword,
        int dwLogonType, int dwLogonProvider, out SafeTokenHandle phToken);

        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
        public extern static bool CloseHandle(IntPtr handle);

        [PermissionSetAttribute(SecurityAction.Demand, Name = "FullTrust")]
        public static void Main(string[] args)
        {
            SafeTokenHandle safeTokenHandle;
            try
            {
                string userName, domainName, password;
                domainName = "domain";
                userName = "username";
                password = "password";
                const int LOGON32_PROVIDER_WINNT50 = 3;
                const int LOGON32_LOGON_NEW_CREDENTIALS = 9;

                bool returnValue = LogonUser(userName, domainName, password, LOGON32_LOGON_NEW_CREDENTIALS, LOGON32_PROVIDER_WINNT50, out safeTokenHandle);

                Console.WriteLine("LogonUser called.");

                if (false == returnValue)
                {
                    int ret = Marshal.GetLastWin32Error();
                    Console.WriteLine("LogonUser failed with error code : {0}", ret);
                    throw new System.ComponentModel.Win32Exception(ret);
                }
                using (safeTokenHandle)
                {
                    Console.WriteLine("Did LogonUser Succeed? " + (returnValue ? "Yes" : "No"));
                    Console.WriteLine("Value of Windows NT token: " + safeTokenHandle);

                    Console.WriteLine("Before impersonation: "
                    + WindowsIdentity.GetCurrent().Name);


                    using (WindowsImpersonationContext impersonatedUser = WindowsIdentity.Impersonate(safeTokenHandle.DangerousGetHandle()))
                    {

                        string src = @"\serversharedfile.txt";
                        string dest = @"c:file.txt";
                        File.Copy(dest, src);

                        Console.WriteLine("After impersonation: "+ WindowsIdentity.GetCurrent().Name);
                    }
                    Console.WriteLine("After closing the context: " + WindowsIdentity.GetCurrent().Name);
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Exception occurred. " + ex.Message);
            }

        }

    }
}

public sealed class SafeTokenHandle : SafeHandleZeroOrMinusOneIsInvalid
{
    private SafeTokenHandle()
        : base(true)
    {
    }

    [DllImport("kernel32.dll")]
    [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
    [SuppressUnmanagedCodeSecurity]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool CloseHandle(IntPtr handle);

    protected override bool ReleaseHandle()
    {
        return CloseHandle(handle);
    }
}