Max Vernon Max Vernon - 5 months ago 29 Question

Impersonate a Windows or Active Directory user from a different, untrusted domain

I need to authenticate against a remote SQL Server using Windows Authentication. The remote SQL Server is running in another domain that does not have a trust relationship with the domain I'm currently logged into via Windows. I cannot use SQL Server authentication since the SQL Server is configured to only trust domain authentication.

Windows itself allows this type of impersonation through the user interface:

enter image description here

I've used

class from
before, but that appears to rely upon the desired username belonging to a trusted domain.

I'm using Visual Studio 2012, and can use up to Microsoft.Net 4.5, with preferably VB, but I can easily convert code from C# if necessary.


For the benefit of future visitors, I'm posting some VB.Net code that allows a process to use NETONLY impersonation to authenticate against a remote server that resides in an untrusted domain:

Option Explicit On
Option Infer Off

Imports System
Imports System.Runtime.InteropServices '   DllImport
Imports System.Security.Principal '  WindowsImpersonationContext

Public Class clsAuthenticator

    ' group type enum
        SecurityAnonymous = 0
        SecurityIdentification = 1
        SecurityImpersonation = 2
        SecurityDelegation = 3
    End Enum

    Public Enum LogonType As Integer
        'This logon type is intended for users who will be interactively using the computer, such as a user being logged on
        'by a terminal server, remote shell, or similar process.
        'This logon type has the additional expense of caching logon information for disconnected operations;
        'therefore, it is inappropriate for some client/server applications,
        'such as a mail server.

        'This logon type is intended for high performance servers to authenticate plaintext passwords.
        'The LogonUser function does not cache credentials for this logon type.

        'This logon type is intended for batch servers, where processes may be executing on behalf of a user without
        'their direct intervention. This type is also for higher performance servers that process many plaintext
        'authentication attempts at a time, such as mail or Web servers.
        'The LogonUser function does not cache credentials for this logon type.
        LOGON32_LOGON_BATCH = 4

        'Indicates a service-type logon. The account provided must have the service privilege enabled.

        'This logon type is for GINA DLLs that log on users who will be interactively using the computer.
        'This logon type can generate a unique audit record that shows when the workstation was unlocked.
        LOGON32_LOGON_UNLOCK = 7

        'This logon type preserves the name and password in the authentication package, which allows the server to make
        'connections to other network servers while impersonating the client. A server can accept plaintext credentials
        'from a client, call LogonUser, verify that the user can access the system across the network, and still
        'communicate with other servers.
        'NOTE: Windows NT:  This value is not supported.

        'This logon type allows the caller to clone its current token and specify new credentials for outbound connections.
        'The new logon session has the same local identifier but uses different credentials for other network connections.
        'NOTE: This logon type is supported only by the LOGON32_PROVIDER_WINNT50 logon provider.
        'NOTE: Windows NT:  This value is not supported.
    End Enum

    Public Enum LogonProvider As Integer
        'Use the standard logon provider for the system.
        'The default security provider is negotiate, unless you pass NULL for the domain name and the user name
        'is not in UPN format. In this case, the default provider is NTLM.
        'NOTE: Windows 2000/NT:   The default security provider is NTLM.
        LOGON32_PROVIDER_WINNT35 = 1
        LOGON32_PROVIDER_WINNT40 = 2
        LOGON32_PROVIDER_WINNT50 = 3
    End Enum

    ' obtains user token
    Declare Auto Function LogonUser Lib "advapi32.dll" (ByVal lpszUsername As String, ByVal lpszDomain As String, ByVal lpszPassword As String, ByVal dwLogonType As LogonType, ByVal dwLogonProvider As LogonProvider, ByRef phToken As IntPtr) As Integer

    ' closes open handles returned by LogonUser
    Declare Function CloseHandle Lib "kernel32.dll" (ByVal handle As IntPtr) As Boolean

    ' creates duplicate token handle
    Declare Auto Function DuplicateToken Lib "advapi32.dll" (ExistingTokenHandle As IntPtr, SECURITY_IMPERSONATION_LEVEL As Int16, ByRef DuplicateTokenHandle As IntPtr) As Boolean

    'WindowsImpersonationContext newUser;
    Private newUser As WindowsImpersonationContext

    ' Attempts to impersonate a user.  If successful, returns 
    ' a WindowsImpersonationContext of the new user's identity.
    ' Username you want to impersonate
    ' Logon domain
    ' User's password to logon with
    Public Sub Impersonator(ByVal sDomain As String, ByVal sUsername As String, ByVal sPassword As String)
        ' initialize tokens

        Dim pExistingTokenHandle As New IntPtr(0)
        Dim pDuplicateTokenHandle As New IntPtr(0)

        If sDomain = "" Then
            sDomain = System.Environment.MachineName
        End If


            Const LOGON32_PROVIDER_DEFAULT As Int32 = 0
            Const LOGON32_LOGON_NEW_CREDENTIALS = 9

            Dim bImpersonated As Boolean = LogonUser(sUsername, sDomain, sPassword, LOGON32_LOGON_NEW_CREDENTIALS, LOGON32_PROVIDER_DEFAULT, pExistingTokenHandle)

            If bImpersonated = False Then
                Dim nErrorCode As Int32 = Marshal.GetLastWin32Error()
                Throw New ApplicationException("LogonUser() failed with error code: " & nErrorCode.ToString)
            End If

            Dim bRetVal As Boolean = DuplicateToken(pExistingTokenHandle, SECURITY_IMPERSONATION_LEVEL.SecurityImpersonation, pDuplicateTokenHandle)
            If bRetVal = False Then
                Dim nErrorCode As Int32 = Marshal.GetLastWin32Error
                Throw New ApplicationException("DuplicateToken() failed with error code: " & nErrorCode)
                Dim newId As New WindowsIdentity(pDuplicateTokenHandle)
                Dim impersonatedUser As WindowsImpersonationContext = newId.Impersonate
                newUser = impersonatedUser
            End If

        Catch ex As Exception

            If pExistingTokenHandle <> IntPtr.Zero Then
            End If
            If pDuplicateTokenHandle <> IntPtr.Zero Then
            End If
        End Try

    End Sub

    Public Sub Undo()
    End Sub
End Class

This can be called from another piece of code like so:

Dim Impersonator As New clsAuthenticator
Dim sDomain as string = "SomeDomain"
Dim sUser as string = "SomeUserName"
Dim sPass as string = "SomePassword"
Impersonator.Impersonator(sDomain, sUser, sPass)
' Run whatever code needs to run against the remote server

The standard warning of not actually embedding passwords in code certainly applies here. In the real world my app obtains the password from an encrypted column in a database.