It’s not uncommon to see a random popup that asks you to “Sign In to iTunes Store” on iOS. They sometimes appear unexpectedly, but they’re usually genuine. However, one developer is warning users not to enter their password when the popup appears in third-party apps.
There is a chance that the app’s developer is phishing for your Apple ID password. Luckily, there’s an easy trick to distinguish legit popups from phishing attempts.