The latest update to the AltStore/AltServer iOS app allows users to sideload their own IPA files without the need for Jailbreak or the worries of possible revokes. AltStore uses a method that exploits the app developer license system to circumvent the potential for revokes. As such, AltStore users can now install any app, even those not on the App Store, on their iPhones permanently.
https://www.notebookcheck.net/You-can-now-sideload-unverified-apps-on-iOS-without-Jailbreak-or-revokes.461039.0.html