Windows Authentication

[primagic]

I am running an application on an intranet.

I am trying to retrieve the windows username but it is returning the application pool username instead.

I have the following in my web.config file:

<system.web>
    <authentication mode="Windows"/>
    <authorization>
      <deny users="?"/>
    </authorization>
  </system.web>

And in IIS the following options for the website:
Anonymous Authentication - disabled
ASP.Net Impersonation - disabled (if I enabled this I get 500 Internal Server Error)
Basic Authentication - disabled
Forms Authentication - disabled
Windows Authentication - Enabled