CFDOCUMENT stops working when I apply HTTP Windows Challenge Authentication

I have an application which generates a PDF document... works great, until I add Windows Authentication.  When I add IIS7 Windows Authentication, it comes back with an error that it has taken longer than allotted time or that the "service is unavailable".  If I remove the IIS7 authentication then it goes back to working just fine.

What am I missing?  I have to secure these web pages, but need CFDOCUMENT to work so the PDFs can be generated.