AppLocker is a tweak that has existed for some time, allowing users to lock individual apps with a password. With iOS 7 and an iPhone 5s, AppLocker is able to lock and unlock apps using Touch ID's fingerprint recognition capabilities. iDownloadBlog has a detailed video of the tweak in use:
AppLocker is only able to access fingerprints that have been entered into the iPhone 5s via the Touch ID menu in the Settings app, and different fingerprints are not distinguished by the system, so there is little setup needed to install the tweak. As demonstrated in the video, app unlocking works as seamlessly as standard device unlocking with Touch ID.
At the current point in time, Touch ID on non-jailbroken devices is limited to unlocking the phone and making purchases in the App Store. It is likely that Apple will expand the use of Touch ID in the future, but it remains unknown whether Apple has plans to release a Touch ID API that would allow the functionality to be built into individual apps as in the AppLocker jailbreak tweak.
The security implications of the Touch ID-supported AppLocker tweak are unknown, as Apple has said that all Touch ID data (in the form of a mathematical representation of a fingerprint) is stored in a "Secure Enclave" inside the A7 processor that is walled off from the rest of iOS and unavailable to iOS or other apps.
According to the developer of the tweak, who spoke to Cult of Mac, AppLocker is not accessing Touch ID data, but rather confirming that a finger is authenticated. "All I am doing is asking iOS, 'Hey, is this finger authenticated?' and I get either a 'Yes' or a 'No,'" he said.
The Touch ID functionality in AppLocker 2.2 is currently available for download on jailbroken devices via the ModMyi repo. The update is free for current AppLocker users and $0.99 for new purchasers.