ImpersonateAsNetworkUser.ps1

#
# Functions to support network user impersonation
#
function Get-ImpersonateLib
{
    if ($script:ImpersonateLib)
    {
        return $script:ImpersonateLib
    }

    $sig = @'
[DllImport("advapi32.dll", SetLastError = true)]
public static extern bool LogonUser(string lpszUsername, string lpszDomain, string lpszPassword, int dwLogonType, int dwLogonProvider, ref IntPtr phToken);

[DllImport("kernel32.dll")]
public static extern Boolean CloseHandle(IntPtr hObject);
'@

   $script:ImpersonateLib = Add-Type -PassThru -Namespace 'Lib.Impersonation' -Name ImpersonationLib -MemberDefinition $sig
   return $script:ImpersonateLib
}

function ImpersonateAs([PSCredential] $cred)
{
    [IntPtr] $userToken = [Security.Principal.WindowsIdentity]::GetCurrent().Token
    $userToken
    $ImpersonateLib = Get-ImpersonateLib
    $bLogin = $ImpersonateLib::LogonUser($cred.GetNetworkCredential().UserName, $cred.GetNetworkCredential().Domain, $cred.GetNetworkCredential().Password, 9, 0, [ref]$userToken)
    if ($bLogin)
    {
        $Identity = New-Object Security.Principal.WindowsIdentity $userToken
        $context = $Identity.Impersonate()
    }
    else
    {
        throw "Can't log on as user '$($cred.GetNetworkCredential().UserName)'."
    }
    $context, $userToken
}

function CloseUserToken([IntPtr] $token)
{
    $ImpersonateLib = Get-ImpersonateLib
    $bLogin = $ImpersonateLib::CloseHandle($token)
    if (!$bLogin)
    {
        throw "Can't close token."
    }
}

# 
# Main Code Block
#

$creds = Get-Credential

try 
{
    ($oldToken, $context, $newToken) = ImpersonateAs -cred $creds
    #
    # Insert code to run as impersonated network user
    #
} 
catch [System.Exception] 
{
    #
    # Catch exceptions
    #
}
finally
{
    # Dispose of impersonated Context
    if ($context)
    {
        $context.Undo()
        $context.Dispose()
        CloseUserToken($newToken)
    }
}