I have a WAB (developer edition, version 2.8) application showing features that have the URL of PDFs in a folder on my IIS10 webserver. When you hit one of the links it opens in a new tab so on the server I do not get any referrer information in IIS. I want to be able to log where the hits to the PDFs are coming from. Ultimately I would like to have the PDFs only available from within the app.