Enterprise Distribution w/ SSO web authentication

I'd like to distribute enterprise .IPA's to other members of our organization. We have a website that sits behind a VPN and requires SSO authentication. Is it possible to distribute IPA's like this?

From my testing, it does not appear to be the case. But perhaps I'm missing something. I've tried putting both the manifest .plist and the .IPA on this website and it does not work. Moving the manifest off-site at least gives a prompt to install, but the install never completes. Only when both the IPA and manifest are off-site, does this seem to work.

My guess is that whatever is handling the itms-services protocol on the phone must not be inheriting the permissions/auth info/cookies from the existing user session. If so, any chance this feature could be added?