-nation/discussions/27755/self-service-ios-asking-for-itunes-login it's probably self service (or another app) trying to auto-install without VPP licenses. Be sure you have VPP licenses for all scoped apps, and be sure you've ticked the tiny box under the VPP tab on every single app your're scoping.
could someone familiar with the authentication system of Moodle could check out the sample code included in this doc and see if it is feasable to create a module that you could add to a course that would generate the token talked about in the pdf file and then pullup itunes correctly?