Impersonator.cs

namespace Tools.Impersonation
{
    using System;
    using System.ComponentModel;
    using System.Runtime.InteropServices;
    using System.Security.Principal;

    /// <summary>
    /// Execute code under another user context.
    /// </summary>
    public class Impersonator : IDisposable
    {
        /// <summary>
        /// Constructor. Starts the impersonation with the given credentials.
        /// </summary>
        /// <param name="userName">The name of the user to act as.</param>
        /// <param name="domainName">The domain name of the user to act as.</param>
        /// <param name="password">The password of the user to act as.</param>
        public Impersonator(string userName, string domainName, string password)
        {
            ImpersonateValidUser(userName, domainName, password);
        }

        protected void Dispose(bool disposing)
        {
            if (disposing)
            {
                impersonationContext?.Undo();
            }
        }

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        #region WinAPI

        [DllImport("advapi32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
        private static extern int LogonUser(
            string lpszUserName,
            string lpszDomain,
            string lpszPassword,
            int dwLogonType,
            int dwLogonProvider,
            ref IntPtr phToken);

        [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern int DuplicateToken(
            IntPtr hToken,
            int impersonationLevel,
            ref IntPtr hNewToken);

        [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern bool RevertToSelf();

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

        private const int LOGON32_LOGON_INTERACTIVE = 2;
        private const int LOGON32_PROVIDER_DEFAULT = 0;

        #endregion

        private WindowsImpersonationContext impersonationContext;

        /// <summary>
        /// Does the actual impersonation.
        /// </summary>
        private void ImpersonateValidUser(string userName, string domain, string password)
        {
            WindowsIdentity tempWindowsIdentity = null;
            IntPtr token = IntPtr.Zero;
            IntPtr tokenDuplicate = IntPtr.Zero;

            try
            {
                if (RevertToSelf())
                {
                    if (LogonUser(
                        userName,
                        domain,
                        password,
                        LOGON32_LOGON_INTERACTIVE,
                        LOGON32_PROVIDER_DEFAULT,
                        ref token) != 0)
                    {
                        if (DuplicateToken(token, 2, ref tokenDuplicate) != 0)
                        {
                            tempWindowsIdentity = new WindowsIdentity(tokenDuplicate);
                            impersonationContext = tempWindowsIdentity.Impersonate();
                        }
                        else
                        {
                            throw new Win32Exception(Marshal.GetLastWin32Error());
                        }
                    }
                    else
                    {
                        throw new Win32Exception(Marshal.GetLastWin32Error());
                    }
                }
                else
                {
                    throw new Win32Exception(Marshal.GetLastWin32Error());
                }
            }
            finally
            {
                if (token != IntPtr.Zero)
                    CloseHandle(token);
                if (tokenDuplicate != IntPtr.Zero)
                    CloseHandle(tokenDuplicate);
            }
        }
    }
}