Impersonation is the concept whereby an application executes under the \
context of the identity of the client that is accessing the \
application. This is achieved by using the access token provided by \
IIS.

Can impersonate entire website by editing the web.config or impersonate chunks of code in the codebehind.
Very usefull when accessing folders on a remote server that has no domain

Impersonate entire website with web.config[-][--][++]

<codebox vbscript>
<%
<identity> Web.config section

The <identity> Web.config section defines what identity (Windows
account) to use when accessing the ASP.NET application. Here is the
generic syntax of the <identity> section of the Web.config:

<identity impersonate="true|false" userName="username" password="password"/>

By default the ASPNET Windows account is used to access ASP.NET
resources through the Aspnet_wp.exe process. This account is less
powerful, compared to the IUSR_ machinename guest Internet account used
by classic ASP for example. In certain situations you might want to use
the anonymous IUSR_ machinename account, as the account accessing your
ASP.NET application and you can do that by using the following code in
your Web.config file:

<system.web>
<identity impersonate="true" />
</system.web>

In this case we use impersonation. In short impersonation is the act of
ASP.NET executing code in the context of an authenticated client
(Windows account).

If you want you can specify a particular account Windows account to be
used instead of the ASPNET Windows account. You can do it like this:

<system.web>
<identity impersonate="true" userName="WindowsDomain\YourUserName" password="YourPassword" />
</system.web>

</codebox>

Impersonate in the Code Behind (ASP.NET)[-][--][++]

Imports[-][--][++]

Imports System.Runtime.InteropServices
Imports System.Security.Principal
Imports System.Web.Security

Script[-][--][++]

<codebox vbscript>
<%
Public LOGON32_LOGON_INTERACTIVE As Integer = 2
Public LOGON32_PROVIDER_DEFAULT As Integer = 0

Public impersonationContext As WindowsImpersonationContext

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

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

Public Sub New()

End Sub

Public 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

Public Sub undoImpersonation()
impersonationContext.Undo()
End Sub
End Class
</codebox>

Impersonate in the Code Behind (C++.NET)[-][--][++]

Imports[-][--][++]

using System.Runtime.InteropServices;
using System.Security.Principal;

Script[-][--][++]

<codebox vbscript>
<%
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 extern bool CloseHandle(IntPtr handle);

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();
}

</codebox>

Calling Impersonate[-][--][++]

Whatever chunk you want to impersonate, just use

if(impersonateValidUser("administrator", "dyna-web2", "password"))
{
    //do stuff with impersonated users here
}
undoImpersonation();