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

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 OnOption Infer OffImports SystemImports System.Runtime.InteropServices '   DllImportImports System.Security.Principal '  WindowsImpersonationContextPublic Class clsAuthenticator    ' group type enum    Enum SECURITY_IMPERSONATION_LEVEL As Int32        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.        LOGON32_LOGON_INTERACTIVE = 2        'This logon type is intended for high performance servers to authenticate plaintext passwords.        'The LogonUser function does not cache credentials for this logon type.        LOGON32_LOGON_NETWORK = 3        '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.        LOGON32_LOGON_SERVICE = 5        '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.        LOGON32_LOGON_NETWORK_CLEARTEXT = 8        '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.        LOGON32_LOGON_NEW_CREDENTIALS = 9    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_DEFAULT = 0        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        Try            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                CloseHandle(pExistingTokenHandle)                Throw New ApplicationException("DuplicateToken() failed with error code: " & nErrorCode)            Else                Dim newId As New WindowsIdentity(pDuplicateTokenHandle)                Dim impersonatedUser As WindowsImpersonationContext = newId.Impersonate                newUser = impersonatedUser            End If        Catch ex As Exception        Finally            If pExistingTokenHandle <> IntPtr.Zero Then                CloseHandle(pExistingTokenHandle)            End If            If pDuplicateTokenHandle <> IntPtr.Zero Then                CloseHandle(pDuplicateTokenHandle)            End If        End Try    End Sub    Public Sub Undo()        newUser.Undo()    End SubEnd Class

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

Dim Impersonator As New clsAuthenticatorDim 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 serverImpersonator.Undo

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.