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public:
virtual System::Security::Principal::WindowsImpersonationContext ^ Impersonate();
public virtual System.Security.Principal.WindowsImpersonationContext Impersonate ();
abstract member Impersonate : unit -> System.Security.Principal.WindowsImpersonationContext
override this.Impersonate : unit -> System.Security.Principal.WindowsImpersonationContext
Public Overridable Function Impersonate () As WindowsImpersonationContext
Returns
Examples
The following example demonstrates how to obtain a Windows account token by calling the unmanaged Win32
LogonUser
function, and how to use that token to impersonate another user and then revert to the original identity.
// This sample demonstrates the use of the WindowsIdentity class to impersonate a user.
// IMPORTANT NOTES:
// This sample requests the user to enter a password on the console screen.
// Because the console window does not support methods allowing the password to be masked,
// it will be visible to anyone viewing the screen.
// On Windows Vista and later this sample must be run as an administrator.
#using <System.dll>
using namespace System;
using namespace System::Runtime::InteropServices;
using namespace System::Security::Principal;
using namespace System::Security::Permissions;
[DllImport("advapi32.dll",SetLastError=true)]
bool LogonUser( String^ lpszUsername, String^ lpszDomain, String^ lpszPassword, int dwLogonType, int dwLogonProvider, IntPtr * phToken );
[DllImport("kernel32.dll",CharSet=CharSet::Auto)]
bool CloseHandle( IntPtr handle );
// Test harness.
// If you incorporate this code into a DLL, be sure to demand FullTrust.
[PermissionSetAttribute(SecurityAction::Demand,Name="FullTrust")]
int main()
IntPtr tokenHandle = IntPtr(0);
String^ userName;
String^ domainName;
// Get the user token for the specified user, domain, and password using the
// unmanaged LogonUser method.
// The local machine name can be used for the domain name to impersonate a user on this machine.
Console::Write( "Enter the name of the domain on which to log on: " );
domainName = Console::ReadLine();
Console::Write( "Enter the login of a user on {0} that you wish to impersonate: ", domainName );
userName = Console::ReadLine();
Console::Write( "Enter the password for {0}: ", userName );
const int LOGON32_PROVIDER_DEFAULT = 0;
//This parameter causes LogonUser to create a primary token.
const int LOGON32_LOGON_INTERACTIVE = 2;
const int SecurityImpersonation = 2;
tokenHandle = IntPtr::Zero;
// Call LogonUser to obtain a handle to an access token.
bool returnValue = LogonUser( userName, domainName, Console::ReadLine(), LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT, &tokenHandle );
Console::WriteLine( "LogonUser called." );
if ( false == returnValue )
int ret = Marshal::GetLastWin32Error();
Console::WriteLine( "LogonUser failed with error code : {0}", ret );
throw gcnew System::ComponentModel::Win32Exception( ret );
Console::WriteLine( "Did LogonUser Succeed? {0}", (returnValue ? (String^)"Yes" : "No") );
Console::WriteLine( "Value of Windows NT token: {0}", tokenHandle );
// Check the identity.
Console::WriteLine( "Before impersonation: {0}", WindowsIdentity::GetCurrent()->Name );
// The token that is passed to the following constructor must
// be a primary token in order to use it for impersonation.
WindowsIdentity^ newId = gcnew WindowsIdentity( tokenHandle );
WindowsImpersonationContext^ impersonatedUser = newId->Impersonate();
// Check the identity.
Console::WriteLine( "After impersonation: {0}", WindowsIdentity::GetCurrent()->Name );
// Stop impersonating the user.
impersonatedUser->Undo();
// Check the identity.
Console::WriteLine( "After Undo: {0}", WindowsIdentity::GetCurrent()->Name );
// Free the tokens.
if ( tokenHandle != IntPtr::Zero )
CloseHandle( tokenHandle );
catch ( Exception^ ex )
Console::WriteLine( "Exception occurred. {0}", ex->Message );
// This sample demonstrates the use of the WindowsIdentity class to impersonate a user.
// IMPORTANT NOTES:
// This sample requests the user to enter a password on the console screen.
// Because the console window does not support methods allowing the password to be masked,
// it will be visible to anyone viewing the screen.
// On Windows Vista and later this sample must be run as an administrator.
using System;
using System.Runtime.InteropServices;
using System.Security.Principal;
using System.Security.Permissions;
using Microsoft.Win32.SafeHandles;
using System.Runtime.ConstrainedExecution;
using System.Security;
public class ImpersonationDemo
[DllImport("advapi32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
public static extern bool LogonUser(String lpszUsername, String lpszDomain, String lpszPassword,
int dwLogonType, int dwLogonProvider, out SafeTokenHandle phToken);
[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
public extern static bool CloseHandle(IntPtr handle);
// Test harness.
// If you incorporate this code into a DLL, be sure to demand FullTrust.
[PermissionSetAttribute(SecurityAction.Demand, Name = "FullTrust")]
public static void Main(string[] args)
SafeTokenHandle safeTokenHandle;
string userName, domainName;
// Get the user token for the specified user, domain, and password using the
// unmanaged LogonUser method.
// The local machine name can be used for the domain name to impersonate a user on this machine.
Console.Write("Enter the name of the domain on which to log on: ");
domainName = Console.ReadLine();
Console.Write("Enter the login of a user on {0} that you wish to impersonate: ", domainName);
userName = Console.ReadLine();
Console.Write("Enter the password for {0}: ", userName);
const int LOGON32_PROVIDER_DEFAULT = 0;
//This parameter causes LogonUser to create a primary token.
const int LOGON32_LOGON_INTERACTIVE = 2;
// Call LogonUser to obtain a handle to an access token.
bool returnValue = LogonUser(userName, domainName, Console.ReadLine(),
LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT,
out safeTokenHandle);
Console.WriteLine("LogonUser called.");
if (false == returnValue)
int ret = Marshal.GetLastWin32Error();
Console.WriteLine("LogonUser failed with error code : {0}", ret);
throw new System.ComponentModel.Win32Exception(ret);
using (safeTokenHandle)
Console.WriteLine("Did LogonUser Succeed? " + (returnValue ? "Yes" : "No"));
Console.WriteLine("Value of Windows NT token: " + safeTokenHandle);
// Check the identity.
Console.WriteLine("Before impersonation: "
+ WindowsIdentity.GetCurrent().Name);
// Use the token handle returned by LogonUser.
using (WindowsIdentity newId = new WindowsIdentity(safeTokenHandle.DangerousGetHandle()))
using (WindowsImpersonationContext impersonatedUser = newId.Impersonate())
// Check the identity.
Console.WriteLine("After impersonation: "
+ WindowsIdentity.GetCurrent().Name);
// Releasing the context object stops the impersonation
// Check the identity.
Console.WriteLine("After closing the context: " + WindowsIdentity.GetCurrent().Name);
catch (Exception ex)
Console.WriteLine("Exception occurred. " + ex.Message);
public sealed class SafeTokenHandle : SafeHandleZeroOrMinusOneIsInvalid
private SafeTokenHandle()
: base(true)
[DllImport("kernel32.dll")]
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
[SuppressUnmanagedCodeSecurity]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool CloseHandle(IntPtr handle);
protected override bool ReleaseHandle()
return CloseHandle(handle);
' This sample demonstrates the use of the WindowsIdentity class to impersonate a user.
' IMPORTANT NOTES:
' This sample requests the user to enter a password on the console screen.
' Because the console window does not support methods allowing the password to be masked,
' it will be visible to anyone viewing the screen.
' On Windows Vista and later this sample must be run as an administrator.
Imports System.Runtime.InteropServices
Imports System.Security.Principal
Imports System.Security.Permissions
Imports Microsoft.Win32.SafeHandles
Imports System.Runtime.ConstrainedExecution
Imports System.Security
Module Module1
Public Class ImpersonationDemo
'Private Declare Auto Function LogonUser Lib "advapi32.dll" (ByVal lpszUsername As [String], _
' ByVal lpszDomain As [String], ByVal lpszPassword As [String], _
' ByVal dwLogonType As Integer, ByVal dwLogonProvider As Integer, _
' ByRef phToken As IntPtr) As Boolean
Private Declare Auto Function LogonUser Lib "advapi32.dll" (ByVal lpszUsername As [String], _
ByVal lpszDomain As [String], ByVal lpszPassword As [String], _
ByVal dwLogonType As Integer, ByVal dwLogonProvider As Integer, _
<Out()> ByRef phToken As SafeTokenHandle) As Boolean
Public Declare Auto Function CloseHandle Lib "kernel32.dll" (ByVal handle As IntPtr) As Boolean
' Test harness.
' If you incorporate this code into a DLL, be sure to demand FullTrust.
<PermissionSetAttribute(SecurityAction.Demand, Name:="FullTrust")> _
Public Overloads Shared Sub Main(ByVal args() As String)
Dim safeTokenHandle As SafeTokenHandle = Nothing
Dim tokenHandle As New IntPtr(0)
Dim userName, domainName As String
' Get the user token for the specified user, domain, and password using the
' unmanaged LogonUser method.
' The local machine name can be used for the domain name to impersonate a user on this machine.
Console.Write("Enter the name of a domain on which to log on: ")
domainName = Console.ReadLine()
Console.Write("Enter the login of a user on {0} that you wish to impersonate: ", domainName)
userName = Console.ReadLine()
Console.Write("Enter the password for {0}: ", userName)
Const LOGON32_PROVIDER_DEFAULT As Integer = 0
'This parameter causes LogonUser to create a primary token.
Const LOGON32_LOGON_INTERACTIVE As Integer = 2
' Call LogonUser to obtain a handle to an access token.
Dim returnValue As Boolean = LogonUser(userName, domainName, Console.ReadLine(), LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT, safeTokenHandle)
Console.WriteLine("LogonUser called.")
If False = returnValue Then
Dim ret As Integer = Marshal.GetLastWin32Error()
Console.WriteLine("LogonUser failed with error code : {0}", ret)
Throw New System.ComponentModel.Win32Exception(ret)
Return
End If
Using safeTokenHandle
Dim success As String
If returnValue Then success = "Yes" Else success = "No"
Console.WriteLine(("Did LogonUser succeed? " + success))
Console.WriteLine(("Value of Windows NT token: " + safeTokenHandle.DangerousGetHandle().ToString()))
' Check the identity.
Console.WriteLine(("Before impersonation: " + WindowsIdentity.GetCurrent().Name))
' Use the token handle returned by LogonUser.
Using newId As New WindowsIdentity(safeTokenHandle.DangerousGetHandle())
Using impersonatedUser As WindowsImpersonationContext = newId.Impersonate()
' Check the identity.
Console.WriteLine(("After impersonation: " + WindowsIdentity.GetCurrent().Name))
' Free the tokens.
End Using
End Using
End Using
Catch ex As Exception
Console.WriteLine(("Exception occurred. " + ex.Message))
End Try
End Sub
End Class
End Module
Public NotInheritable Class SafeTokenHandle
Inherits SafeHandleZeroOrMinusOneIsInvalid
Private Sub New()
MyBase.New(True)
End Sub
Private Declare Auto Function LogonUser Lib "advapi32.dll" (ByVal lpszUsername As [String], _
ByVal lpszDomain As [String], ByVal lpszPassword As [String], _
ByVal dwLogonType As Integer, ByVal dwLogonProvider As Integer, _
ByRef phToken As IntPtr) As Boolean
<DllImport("kernel32.dll"), ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success), SuppressUnmanagedCodeSecurity()> _
Private Shared Function CloseHandle(ByVal handle As IntPtr) As <MarshalAs(UnmanagedType.Bool)> Boolean
End Function
Protected Overrides Function ReleaseHandle() As Boolean
Return CloseHandle(handle)
End Function 'ReleaseHandle
End Class
Remarks
On Windows NT platforms, the current user must have sufficient rights to allow impersonation.
Warning
Avoid using this method with the async/await pattern. In some cases it may lead to reliability issues due to impersonation not being reverted even if the resulting
WindowsImpersonationContext
is disposed. Use
RunImpersonated
instead.
public:
static System::Security::Principal::WindowsImpersonationContext ^ Impersonate(IntPtr userToken);
public static System.Security.Principal.WindowsImpersonationContext Impersonate (IntPtr userToken);
static member Impersonate : nativeint -> System.Security.Principal.WindowsImpersonationContext
Public Shared Function Impersonate (userToken As IntPtr) As WindowsImpersonationContext
Parameters
The handle of a Windows account token. This token is usually retrieved through a call to unmanaged code, such as a call to the Windows API
LogonUser
function.
Returns
Examples
The following example demonstrates how to obtain a Windows account token by calling the unmanaged Win32
LogonUser
function, and how to use that token to impersonate another user and then revert to the original identity.
// This sample demonstrates the use of the WindowsIdentity class to impersonate a user.
// IMPORTANT NOTES:
// This sample requests the user to enter a password on the console screen.
// Because the console window does not support methods allowing the password to be masked,
// it will be visible to anyone viewing the screen.
// On Windows Vista and later this sample must be run as an administrator.
using System;
using System.Runtime.InteropServices;
using System.Security.Principal;
using System.Security.Permissions;
using Microsoft.Win32.SafeHandles;
using System.Runtime.ConstrainedExecution;
using System.Security;
public class ImpersonationDemo
[DllImport("advapi32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
public static extern bool LogonUser(String lpszUsername, String lpszDomain, String lpszPassword,
int dwLogonType, int dwLogonProvider, out SafeTokenHandle phToken);
[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
public extern static bool CloseHandle(IntPtr handle);
// Test harness.
// If you incorporate this code into a DLL, be sure to demand FullTrust.
[PermissionSetAttribute(SecurityAction.Demand, Name = "FullTrust")]
public static void Main(string[] args)
SafeTokenHandle safeTokenHandle;
string userName, domainName;
// Get the user token for the specified user, domain, and password using the
// unmanaged LogonUser method.
// The local machine name can be used for the domain name to impersonate a user on this machine.
Console.Write("Enter the name of the domain on which to log on: ");
domainName = Console.ReadLine();
Console.Write("Enter the login of a user on {0} that you wish to impersonate: ", domainName);
userName = Console.ReadLine();
Console.Write("Enter the password for {0}: ", userName);
const int LOGON32_PROVIDER_DEFAULT = 0;
//This parameter causes LogonUser to create a primary token.
const int LOGON32_LOGON_INTERACTIVE = 2;
// Call LogonUser to obtain a handle to an access token.
bool returnValue = LogonUser(userName, domainName, Console.ReadLine(),
LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT,
out safeTokenHandle);
Console.WriteLine("LogonUser called.");
if (false == returnValue)
int ret = Marshal.GetLastWin32Error();
Console.WriteLine("LogonUser failed with error code : {0}", ret);
throw new System.ComponentModel.Win32Exception(ret);
using (safeTokenHandle)
Console.WriteLine("Did LogonUser Succeed? " + (returnValue ? "Yes" : "No"));
Console.WriteLine("Value of Windows NT token: " + safeTokenHandle);
// Check the identity.
Console.WriteLine("Before impersonation: "
+ WindowsIdentity.GetCurrent().Name);
// Use the token handle returned by LogonUser.
using (WindowsImpersonationContext impersonatedUser = WindowsIdentity.Impersonate(safeTokenHandle.DangerousGetHandle()))
// Check the identity.
Console.WriteLine("After impersonation: "
+ WindowsIdentity.GetCurrent().Name);
// Releasing the context object stops the impersonation
// Check the identity.
Console.WriteLine("After closing the context: " + WindowsIdentity.GetCurrent().Name);
catch (Exception ex)
Console.WriteLine("Exception occurred. " + ex.Message);
public sealed class SafeTokenHandle : SafeHandleZeroOrMinusOneIsInvalid
private SafeTokenHandle()
: base(true)
[DllImport("kernel32.dll")]
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
[SuppressUnmanagedCodeSecurity]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool CloseHandle(IntPtr handle);
protected override bool ReleaseHandle()
return CloseHandle(handle);
' This sample demonstrates the use of the WindowsIdentity class to impersonate a user.
' IMPORTANT NOTES:
' This sample requests the user to enter a password on the console screen.
' Because the console window does not support methods allowing the password to be masked,
' it will be visible to anyone viewing the screen.
' On Windows Vista and later this sample must be run as an administrator.
Imports System.Runtime.InteropServices
Imports System.Security.Principal
Imports System.Security.Permissions
Imports Microsoft.Win32.SafeHandles
Imports System.Runtime.ConstrainedExecution
Imports System.Security
Module Module1
Public Class ImpersonationDemo
'Private Declare Auto Function LogonUser Lib "advapi32.dll" (ByVal lpszUsername As [String], _
' ByVal lpszDomain As [String], ByVal lpszPassword As [String], _
' ByVal dwLogonType As Integer, ByVal dwLogonProvider As Integer, _
' ByRef phToken As IntPtr) As Boolean
Private Declare Auto Function LogonUser Lib "advapi32.dll" (ByVal lpszUsername As [String], _
ByVal lpszDomain As [String], ByVal lpszPassword As [String], _
ByVal dwLogonType As Integer, ByVal dwLogonProvider As Integer, _
<Out()> ByRef phToken As SafeTokenHandle) As Boolean
Public Declare Auto Function CloseHandle Lib "kernel32.dll" (ByVal handle As IntPtr) As Boolean
' Test harness.
' If you incorporate this code into a DLL, be sure to demand FullTrust.
<PermissionSetAttribute(SecurityAction.Demand, Name:="FullTrust")> _
Public Overloads Shared Sub Main(ByVal args() As String)
Dim safeTokenHandle As SafeTokenHandle
Dim tokenHandle As New IntPtr(0)
Dim userName, domainName As String
' Get the user token for the specified user, domain, and password using the
' unmanaged LogonUser method.
' The local machine name can be used for the domain name to impersonate a user on this machine.
Console.Write("Enter the name of a domain on which to log on: ")
domainName = Console.ReadLine()
Console.Write("Enter the login of a user on {0} that you wish to impersonate: ", domainName)
userName = Console.ReadLine()
Console.Write("Enter the password for {0}: ", userName)
Const LOGON32_PROVIDER_DEFAULT As Integer = 0
'This parameter causes LogonUser to create a primary token.
Const LOGON32_LOGON_INTERACTIVE As Integer = 2
' Call LogonUser to obtain a handle to an access token.
Dim returnValue As Boolean = LogonUser(userName, domainName, Console.ReadLine(), LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT, safeTokenHandle)
Console.WriteLine("LogonUser called.")
If False = returnValue Then
Dim ret As Integer = Marshal.GetLastWin32Error()
Console.WriteLine("LogonUser failed with error code : {0}", ret)
Throw New System.ComponentModel.Win32Exception(ret)
Return
End If
Using safeTokenHandle
Dim success As String
If returnValue Then success = "Yes" Else success = "No"
Console.WriteLine(("Did LogonUser succeed? " + success))
Console.WriteLine(("Value of Windows NT token: " + safeTokenHandle.DangerousGetHandle().ToString()))
' Check the identity.
Console.WriteLine(("Before impersonation: " + WindowsIdentity.GetCurrent().Name))
' Use the token handle returned by LogonUser.
Using impersonatedUser As WindowsImpersonationContext = WindowsIdentity.Impersonate(safeTokenHandle.DangerousGetHandle())
' Check the identity.
Console.WriteLine(("After impersonation: " + WindowsIdentity.GetCurrent().Name))
' Free the tokens.
End Using
End Using
Catch ex As Exception
Console.WriteLine(("Exception occurred. " + ex.Message))
End Try
End Sub
End Class
End Module
Public NotInheritable Class SafeTokenHandle
Inherits SafeHandleZeroOrMinusOneIsInvalid
Private Sub New()
MyBase.New(True)
End Sub
Private Declare Auto Function LogonUser Lib "advapi32.dll" (ByVal lpszUsername As [String], _
ByVal lpszDomain As [String], ByVal lpszPassword As [String], _
ByVal dwLogonType As Integer, ByVal dwLogonProvider As Integer, _
ByRef phToken As IntPtr) As Boolean
<DllImport("kernel32.dll"), ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success), SuppressUnmanagedCodeSecurity()> _
Private Shared Function CloseHandle(ByVal handle As IntPtr) As <MarshalAs(UnmanagedType.Bool)> Boolean
End Function
Protected Overrides Function ReleaseHandle() As Boolean
Return CloseHandle(handle)
End Function 'ReleaseHandle
End Class
Remarks
On Windows NT platforms, the current user must have sufficient rights to allow impersonation.
Calling the
Impersonate(IntPtr)
method with a
userToken
value of
Zero
is equivalent to calling the Win32
RevertToSelf
function. If another user is currently being impersonated, control reverts to the original user.
For more information about calls to unmanaged code, see
Consuming Unmanaged DLL Functions
.
Warning
Avoid using this method with the async/await pattern. In some cases it may lead to reliability issues due to impersonation not being reverted even if the resulting
WindowsImpersonationContext
is disposed. Use
RunImpersonated
instead.
