Allows you to execute code under another user's privileges.

Impersonator.cs

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

namespace JakeWharton
{
    public class Impersonator : IDisposable
    {
        private WindowsImpersonationContext ImpersonatedUser = null;
        private IntPtr UserHandle;

        public Impersonator(string Username, string Domain, string Password)
        {
            this.UserHandle = new IntPtr(0);

            if (!Impersonator.LogonUser(Username, Domain, Password, Impersonator.LOGON32_LOGON_INTERACTIVE,
                                        Impersonator.LOGON32_PROVIDER_DEFAULT, ref this.UserHandle))
            {
                throw new ApplicationException(string.Format("Could not impersonate user \"{0}\\{1}\".", Domain, Username));
            }

            this.ImpersonatedUser = (new WindowsIdentity(this.UserHandle)).Impersonate();
        }

        #region IDisposable Members
        public void Dispose()
        {
            if (this.ImpersonatedUser != null)
            {
                this.ImpersonatedUser.Undo();
                Impersonator.CloseHandle(UserHandle);
            }
        }
        #endregion

        #region Interoperability
        public const int LOGON32_LOGON_INTERACTIVE = 2;
        public const int LOGON32_LOGON_SERVICE     = 3;
        public const int LOGON32_PROVIDER_DEFAULT  = 0;

        [DllImport("advapi32.dll", CharSet = CharSet.Auto)]
        public static extern bool LogonUser(String lpszUserName, String lpszDomain, String lpszPassword, int dwLogonType, int dwLogonProvider, ref IntPtr phToken);

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