I'm not sure how sophisticated the App Store review process is now, but it would be quite easy to grep the codebase for any UIAlertView with the word "password"

I'm not sure how sophisticated the App Store review process is now, but it would be quite easy to grep the codebase for any UIAlertView with the word "password" or "sign in" inside it (unless it did some sort of real-time decrypting of that message). Regardless, iOS should have a private alert view for inputting sensitive data, similar to the Touch ID prompt. If the prompt is not even relevant to the app container, it should also completely minimize the app view to prevent confusion.