Click here to Skip to main content
15,867,568 members
Articles / Programming Languages / C#
Article

Windows Impersonation using C#

Rate me:
Please Sign up or sign in to vote.
4.77/5 (49 votes)
29 Apr 2003CPOL 720.4K   15.6K   149   74
An article demonstrating how to use Windows impersonation in your C# code

Impersonation

Introduction

I've been a member of the CodeProject for over 3 years now, and still haven't contributed any articles - until now.

While designing a Windows Forms-based application, to administrate containers in our Active Directory, I needed a way to allow binding to the AD using alternate credentials. Windows impersonation was the answer. This sample app demonstrates how to use unmanaged code by calling LogonUser() contained within the advapi32.dll, and pass a token handle back to your .NET application using WindowsImpersonationContext.

One of the downfalls to the LogonUser()function is that the password get passed in clear-text.

Partial Source Code

C#
using System.Runtime.InteropServices; // DllImport
using System.Security.Principal; // WindowsImpersonationContext
using System.Security.Permissions; // PermissionSetAttribute
...

public WindowsImpersonationContext 
    ImpersonateUser(string sUsername, string sDomain, string sPassword)
{
    // initialize tokens
    IntPtr pExistingTokenHandle = new IntPtr(0);
    IntPtr pDuplicateTokenHandle = new IntPtr(0);
    pExistingTokenHandle = IntPtr.Zero;
    pDuplicateTokenHandle = IntPtr.Zero;
    
    // if domain name was blank, assume local machine
    if (sDomain == "")
        sDomain = System.Environment.MachineName;

    try
    {
        string sResult = null;

        const int LOGON32_PROVIDER_DEFAULT = 0;

        // create token
        const int LOGON32_LOGON_INTERACTIVE = 2;
        //const int SecurityImpersonation = 2;

        // get handle to token
        bool bImpersonated = LogonUser(sUsername, sDomain, sPassword, 
            LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT, 
                ref pExistingTokenHandle);

        // did impersonation fail?
        if (false == bImpersonated)
        {
            int nErrorCode = Marshal.GetLastWin32Error();
            sResult = "LogonUser() failed with error code: " + 
                nErrorCode + "\r\n";

            // show the reason why LogonUser failed
            MessageBox.Show(this, sResult, "Error", 
                MessageBoxButtons.OK, MessageBoxIcon.Error);
        }

        // Get identity before impersonation
        sResult += "Before impersonation: " + 
            WindowsIdentity.GetCurrent().Name + "\r\n";

        bool bRetVal = DuplicateToken(pExistingTokenHandle, 
            (int)SECURITY_IMPERSONATION_LEVEL.SecurityImpersonation, 
                ref pDuplicateTokenHandle);

        // did DuplicateToken fail?
        if (false == bRetVal)
        {
            int nErrorCode = Marshal.GetLastWin32Error();
            // close existing handle
            CloseHandle(pExistingTokenHandle); 
            sResult += "DuplicateToken() failed with error code: " 
                + nErrorCode + "\r\n";

            // show the reason why DuplicateToken failed
            MessageBox.Show(this, sResult, "Error", 
                MessageBoxButtons.OK, MessageBoxIcon.Error);
            return null;
        }
        else
        {
            // create new identity using new primary token
            WindowsIdentity newId = new WindowsIdentity
                                        (pDuplicateTokenHandle);
            WindowsImpersonationContext impersonatedUser = 
                                        newId.Impersonate();

            // check the identity after impersonation
            sResult += "After impersonation: " + 
                WindowsIdentity.GetCurrent().Name + "\r\n";
            
            MessageBox.Show(this, sResult, "Success", 
                MessageBoxButtons.OK, MessageBoxIcon.Information);
            return impersonatedUser;
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }
    finally
    {
        // close handle(s)
        if (pExistingTokenHandle != IntPtr.Zero)
            CloseHandle(pExistingTokenHandle);
        if (pDuplicateTokenHandle != IntPtr.Zero) 
            CloseHandle(pDuplicateTokenHandle);
    }
}

Points of Interest

This code won't work on Windows 98 or ME because they do not utilize user tokens. Code was built and run using Visual Studio.NET 2002 on Windows XP Service Pack 1.

One of the other uses for this code I've found is, for instantiating COM components that must run in an alternate security context to that of the logged-on user.

If anyone has a more secure method of achieving the same thing, please let me know.

History

  • Version 1.0 - 04.25.03 - First release version

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Zambia Zambia
Living abroad and loving life.

Comments and Discussions

 
GeneralWIndows 7 Pin
moralam13-Jul-10 7:58
moralam13-Jul-10 7:58 
GeneralRe: WIndows 7 Pin
Christian Merritt28-Jan-13 5:25
Christian Merritt28-Jan-13 5:25 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Praise Praise    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.