Step Two is the best two-step verification app for iPhone and iPad.

Features

iCloud

Never get locked out of your own accounts. Step Two uses iCloud to securely back up your two-step codes and make them available on all your devices.

Design

Security shouldn’t come at the expense of usability. Step Two’s friendly, intuitive, and accessible interface makes using two-step verification easier than ever. 

Works with Most Online Accounts

Step Two works with any online account that uses time-based one-time passwords (TOTP) for two-step verification, such as Google, Twitter, Amazon, and many more.