仅在运行代码的特定部分时模拟特定用户

本文引用下面的 Microsoft .NET Framework 类库命名空间：

•	System.Web.Security
•	System.Security.Principal
•	System.Runtime.InteropServices

Dim LOGON32_LOGON_INTERACTIVE As Integer = 2
Dim LOGON32_PROVIDER_DEFAULT As Integer = 0

Dim impersonationContext As WindowsImpersonationContext

Declare Function LogonUserA()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 Integer

Declare Auto Function DuplicateToken()Function DuplicateToken Lib "advapi32.dll" ( _
ByVal ExistingTokenHandle As IntPtr, _
ByVal ImpersonationLevel As Integer, _
ByRef DuplicateTokenHandle As IntPtr) As Integer

Declare Auto Function RevertToSelf()Function RevertToSelf Lib "advapi32.dll" () As Long
Declare Auto Function CloseHandle()Function CloseHandle Lib "kernel32.dll" (ByVal handle As IntPtr) As Long

Public Sub Page_Load()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 If
End Sub

Private Function impersonateValidUser()Function impersonateValidUser(ByVal userName As String, _
ByVal domain As String, ByVal password As String) As Boolean

Dim tempWindowsIdentity As WindowsIdentity
Dim token As IntPtr = IntPtr.Zero
Dim tokenDuplicate As IntPtr = IntPtr.Zero
impersonateValidUser = False

If RevertToSelf() Then
If LogonUserA(userName, domain, password, LOGON32_LOGON_INTERACTIVE,
LOGON32_PROVIDER_DEFAULT, token) <> 0 Then
If DuplicateToken(token, 2, tokenDuplicate) <> 0 Then
tempWindowsIdentity = New WindowsIdentity(tokenDuplicate)
impersonationContext = tempWindowsIdentity.Impersonate()
If Not impersonationContext Is Nothing Then
impersonateValidUser = True
End If
End If
End If
End If
If Not tokenDuplicate.Equals(IntPtr.Zero) Then
CloseHandle(tokenDuplicate)
End If
If Not token.Equals(IntPtr.Zero) Then
CloseHandle(token)
End If
End Function

Private Sub undoImpersonation()Sub undoImpersonation()
impersonationContext.Undo()
End Sub

以前用 Web.config 文件的 <identity> 标记，还是改成这种比较安全。
原文地址：http://support.microsoft.com/default.aspx?scid=kb;zh-cn;306158#4