I tried to do something as a test. I downloaded a simple IPA file from the iTunes (via MacBook).
After this was done, I tried to install it locally. The app installed successfully but on the first run it required authentication for the AppStore.
Any thoughts?
Every IPA file you download includes information about the Apple ID account used to purchase that app. When you install from out of the App Store, the operating system (iOS) first checks if you have authorization to use it, and it will not allow you to execute it if you don't (you enter an Apple ID different from the one indicated by the IPA file, or you don't know the password).
This post from Ask Different indicates how to modify the Apple ID of an IPA file (basically you rename it from .ipa to .zip, inside there is a file called iTunesMetatdata.plist that contains a field appleId that you can change). You'll still have to identify and if you haven't purchased that app you won't be able to run it.