I am a DNN noob... so forgive me if this is a stupid question... 

I have inherited a portal where users are required to log in using DNN user IDs... within my portals, it serves up pages (via iframes) from various web apps and web sites on our IIS servers... the users accessing the portal do not currently have active directory accounts on our network... but I need to secure our web sites so that the web pages, PDFs and Docs and everything else that can be accessed within our portal can only be accessed by an authenticated user... 

In a test (and I'm not 100% sure this is the right way, or easiest way to handle this problem) I changed one of the web apps to require Windows authentication... now, after I log into the portal, when I navigate to that page it prompts me for credentials for my network... which is sort of what I want... however, I would like it to not prompt for the network credentials... I would like to setup DNN to use a default active directory account to authenticate to these web pages... so that the user isn't prompted for AD credentials if they have already authenticated through DNN... but if they are not already authenticated through DNN... then I want it to prompt them for AD credentials... 

Does this make sense?  Any guidance would be greatly appreciated...