How to implement impersonation in an ASP.NET application
Symptoms
This article describes different ways to implement impersonation in an ASP.NET application.
Resolution
If you want to impersonate a user on a thread in ASP.NET, you can use one of the following methods, based on your requirments: Impersonate the IIS authenticated account or userImpersonate a specific user for all the requests of an ASP.NET application Impersonate the authenticating user in codeImpersonate a specific user in codeNote You can use the following code to determine what user the thread is executing as:
System.Security.Principal.WindowsIdentity.GetCurrent().Name
Impersonate the IIS Authenticated Account or User To impersonate the Microsoft Internet Information Services (IIS) authenticating user on every request for every page in an ASP.NET application, you must include an <identity> tag in the Web.config file of this application and set the impersonate attribute to true. For example:
<identity impersonate=”true” />
Impersonate a Specific User for All the Requests of an ASP.NET Application To impersonate a specific user for all the requests on all pages of an ASP.NET application, you can specify the userName and password attributes in the <identity> tag of the Web.config file for that application. For example:
<identity impersonate=”true” userName=”accountname” password=”password” /> Note The identity of the process that impersonates a specific user on a thread must have the “Act as part of the operating system” privilege. By default, the Aspnet_wp.exe process runs under a computer account named ASPNET. However, this account does not have the required privileges to impersonate a specific user. You receive an error message if you try to impersonate a specific user. This information applies only to the .NET Framework 1.0. This privilege is not required for the .NET Framework 1.1.
To work around this problem, use one of the following methods: Grant the “Act as part of the operating system” privilege to the ASPNET account (the least privileged account).
Note Although you can use this method to work around the problem, Microsoft does not recommend this method.Change the account that the Aspnet_wp.exe process runs under to the System account in the <processModel> configuration section of the Machine.config file.
Impersonate the Authenticating User in Code To impersonate the authenticating user (User.Identity) only when you run a particular section of code, you can use the code to follow. This method requires that the authenticating user identity is of type WindowsIdentity.
Visual Basic .NET
Dim impersonationContext As System.Security.Principal.WindowsImpersonationContextDim currentWindowsIdentity As System.Security.Principal.WindowsIdentitycurrentWindowsIdentity = CType(User.Identity, System.Security.Principal.WindowsIdentity)impersonationContext = currentWindowsIdentity.Impersonate()’Insert your code that runs under the security context of the authenticating user here.impersonationContext.Undo() Visual C# .NET
System.Security.Principal.WindowsImpersonationContext impersonationContext;impersonationContext =((System.Security.Principal.WindowsIdentity)User.Identity).Impersonate();//Insert your code that runs under the security context of the authenticating user here.impersonationContext.Undo(); Visual J# .NET
System.Security.Principal.WindowsImpersonationContext impersonationContext;impersonationContext =((System.Security.Principal.WindowsIdentity)get_User().get_Identity()).Impersonate();//Insert your code that runs under the security context of the authenticating user here.impersonationContext.Undo();
Impersonate a Specific User in Code To impersonate a specific user only when you run a particular section of code, use the following code:
Visual Basic .NET
<%@ Page Language=”VB” %><%@ Import Namespace = “System.Web” %><%@ Import Namespace = “System.Web.Security” %><%@ Import Namespace = “System.Security.Principal” %><%@ Import Namespace = “System.Runtime.InteropServices” %><script runat=server>Dim LOGON32_LOGON_INTERACTIVE As Integer = 2Dim LOGON32_PROVIDER_DEFAULT As Integer = 0Dim impersonationContext As WindowsImpersonationContextDeclare Function LogonUserA 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 IntegerDeclare Auto Function DuplicateToken Lib “advapi32.dll” ( _ByVal ExistingTokenHandle As IntPtr, _ByVal ImpersonationLevel As Integer, _ByRef DuplicateTokenHandle As IntPtr) As IntegerDeclare Auto Function RevertToSelf Lib “advapi32.dll” () As LongDeclare Auto Function CloseHandle Lib “kernel32.dll” (ByVal handle As IntPtr) As LongPublic Sub Page_Load(ByVal s As Object, ByVal e As EventArgs)If impersonateValidUser(“username”, “domain”, “password”) Then’Insert your code that runs under the security context of a specific user here.undoImpersonation()Else’Your impersonation failed. Therefore, include a fail-safe mechanism here.End IfEnd SubPrivate Function impersonateValidUser(ByVal userName As String, _ByVal domain As String, ByVal password As String) As BooleanDim tempWindowsIdentity As WindowsIdentityDim token As IntPtr = IntPtr.ZeroDim tokenDuplicate As IntPtr = IntPtr.ZeroimpersonateValidUser = FalseIf RevertToSelf() ThenIf LogonUserA(userName, domain, password, LOGON32_LOGON_INTERACTIVE,LOGON32_PROVIDER_DEFAULT, token) <> 0 ThenIf DuplicateToken(token, 2, tokenDuplicate) <> 0 ThentempWindowsIdentity = New WindowsIdentity(tokenDuplicate)impersonationContext = tempWindowsIdentity.Impersonate()If Not impersonationContext Is Nothing ThenimpersonateValidUser = TrueEnd IfEnd IfEnd IfEnd IfIf Not tokenDuplicate.Equals(IntPtr.Zero) ThenCloseHandle(tokenDuplicate)End IfIf Not token.Equals(IntPtr.Zero) ThenCloseHandle(token)End IfEnd FunctionPrivate Sub undoImpersonation()impersonationContext.Undo()End Sub</script>Visual C# .NET
<%@ Page Language=”C#”%><%@ Import Namespace = “System.Web” %><%@ Import Namespace = “System.Web.Security” %><%@ Import Namespace = “System.Security.Principal” %><%@ Import Namespace = “System.Runtime.InteropServices” %><script runat=server>public const int LOGON32_LOGON_INTERACTIVE = 2;public const int LOGON32_PROVIDER_DEFAULT = 0;WindowsImpersonationContext impersonationContext; [DllImport("advapi32.dll")]public static extern int LogonUserA(String lpszUserName, String lpszDomain, String lpszPassword, int dwLogonType, int dwLogonProvider, ref IntPtr phToken);[DllImport("advapi32.dll", CharSet=CharSet.Auto, SetLastError=true)]public static extern int DuplicateToken(IntPtr hToken, int impersonationLevel, ref IntPtr hNewToken);[DllImport("advapi32.dll", CharSet=CharSet.Auto, SetLastError=true)]public static extern bool RevertToSelf();[DllImport("kernel32.dll", CharSet=CharSet.Auto)]public static externbool CloseHandle(IntPtr handle);public void Page_Load(Object s, EventArgs e){ if(impersonateValidUser(“username”, “domain”, “password”)) { //Insert your code that runs under the security context of a specific user here. undoImpersonation(); } else { //Your impersonation failed. Therefore, include a fail-safe mechanism here. }}private bool impersonateValidUser(String userName, String domain, String password){ WindowsIdentity tempWindowsIdentity; IntPtr token = IntPtr.Zero; IntPtr tokenDuplicate = IntPtr.Zero; if(RevertToSelf()) { if(LogonUserA(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(); if (impersonationContext != null) { CloseHandle(token); CloseHandle(tokenDuplicate); return true; } } } } if(token!= IntPtr.Zero) CloseHandle(token); if(tokenDuplicate!=IntPtr.Zero) CloseHandle(tokenDuplicate); return false;}private void undoImpersonation(){ impersonationContext.Undo();}</script>Visual J# .NET
<%@ Page language=”VJ#” %><%@ Import Namespace=”System.Web” %><%@ Import Namespace=”System.Web.Security” %><%@ Import Namespace=”System.Security.Principal” %><%@ Import Namespace=”System.Runtime.InteropServices” %><script runat=server>public static int LOGON32_LOGON_INTERACTIVE = 2;public static int LOGON32_PROVIDER_DEFAULT = 0;WindowsImpersonationContext impersonationContext; /** @attribute DllImport(“advapi32.dll”) */ public static native int LogonUserA(String lpszUserName, String lpszDomain, String lpszPassword, int dwLogonType, int dwLogonProvider, System.IntPtr[] phToken);/** @attribute DllImport(“advapi32.dll”, CharSet=CharSet.Auto, SetLastError=true) */ public static native int DuplicateToken(System.IntPtr hToken, int impersonationLevel, System.IntPtr[] hNewToken);/** @attribute DllImport(“kernel32.dll”,CharSet=CharSet.Auto) */ public static nativeboolean CloseHandle(System.IntPtr[] handle);/** @attribute DllImport(“advapi32.dll”, CharSet=CharSet.Auto,SetLastError=true) */ public static native boolean RevertToSelf();public void Page_Load(Object s, System.EventArgs e){ if(impersonateValidUser(“username”, “domain”, ” password”)) { //Insert your code that runs under the security context of a specific user here. undoImpersonation(); } else { //Your impersonation failed. Therefore, include a fail-safe mechanism here. }}private boolean impersonateValidUser(String userName, String domain, String password){ WindowsIdentity tempWindowsIdentity; System.IntPtr[] token = new System.IntPtr[1]; System.IntPtr[] tokenDuplicate = new System.IntPtr[1]; if(RevertToSelf()) { if(LogonUserA(userName, domain, password, LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT, token) != 0) { if(DuplicateToken(token[0], 2, tokenDuplicate) != 0) { tempWindowsIdentity = new WindowsIdentity(tokenDuplicate[0]); impersonationContext = tempWindowsIdentity.Impersonate(); if (impersonationContext != null) { CloseHandle(tokenDuplicate); CloseHandle(token); return true; } } } } if(!token[0].Equals(System.IntPtr.Zero)) CloseHandle(token); if(!tokenDuplicate[0].Equals(System.IntPtr.Zero)) CloseHandle(tokenDuplicate); return false;}private void undoImpersonation(){ impersonationContext.Undo();}</script> Note The identity of the process that impersonates a specific user on a thread must have the “Act as part of the operating system” privilege if the Aspnet_wp.exe process is running on a Microsoft Windows 2000-based computer. The “Act as part of the operating system” privilege is not required if the Aspnet_wp.exe process is running on a Windows XP-based computer or on a Windows Server 2003-based computer. By default, the Aspnet_wp.exe process runs under a computer account named ASPNET. However, this account does not have the required privileges to impersonate a specific user. You receive an error message if you try to impersonate a specific user. .
To work around this problem, use one of the following methods: Grant the “Act as part of the operating system” privilege to the ASPNET account.
Note We do not recommend this method to work around the problem.Change the account that the Aspnet_wp.exe process runs under to the System account in the <processModel> configuration section of the Machine.config file.