Geoffrey ,
Did you add the downloaded files from AGOL as an application in your IIS or your site root folder (wwwroot)?, if you did that of IIS then make sure you do this set up as illustrated below, however if otherwise then it should just work@@:
1. Click on the basic settings as in figure below on the right side of your IIS Manager:
2. Connect As: using the "Specific User" (Preferably an admin account that never changes)
3. Test setting: Make sure the result are ticked green
Now you can test your site......Hope this is useful