This happens on all iOS devices, regardless of whether it is running iOS 6 or iOS 7.
On the 0.8.0 release you can enter your information into the sign-in fields and the game will act as if you are signed in, but you are unable to Play on Realms (the button is still absent) and the "Sign Out" button is unresponsive. The process repeats if you end the app's process through the multitasking bar.
EDIT: Fixed in 0.8.1.