How to monitor a web site with login prompt?

I am trying to create an application monitor that will check a web page that has a windows login prompt on it. Unfortunately, this is not a simple forms-based login, so none of the component monitors seem to be working (HTTP Monitor or HTTPS form login Monitor) .

I also tried looking at building my own with PowerShell, using the "Invoke-WebRequest" commandlet, and that won't do it either (because of the login prompt).

How can I make a simple web page test that will enter the credentials when prompted?

Thanks

-P