It’s now a safe bet that Apple’s next iPhone will sport a fingerprint scanner.

We’ve heard the rumors, read the tea leaves from Apple’s purchase of Authentec, and seen the distinctive metal ring around the supposed iPhone 5S boxes (which is said to house the fingerprint scanner). And now, on the eve of the next iPhone’s launch, the Wall Street Journal is pointing to two sources who claim that the fingerprint scanner is indeed real.

There are plenty of potential use cases for a fingerprint sensor in your smartphone, from making it easier to unlock the phone, to adding another level of security to your mobile wallet. The sensor would be the equivalent to the introduction of Siri in the iPhone 4S — it’s not an Earth-shattering feature, but it’s one that clearly distinguishes the slightly refreshed phone from its predecessor.

Apple is expected to unveil the iPhone 5S tomorrow, which, like the iPhone 3GS and 4S, would look a lot like last year’s iPhone 5 with better hardware. Additionally, Apple could reveal the cheaper iPhone 5C tomorrow, which is said to sport cases in many colors.

The WSJ’s report claims that the fingerprint sensor would be available “on the more expensive of two iPhones” Apple is expected to unveil, which means the unveiling of the anticipated cheaper iPhone — the iPhone 5C — is a pretty safe bet as well.

Previous reports noted that the iPhone 5S would feature a convex home button, which faces outward to better scan your thumb. Apple has so far only used concave home buttons in the iPhone, which curve inward. The iPhone 5S is also expected to get a slightly improved camera, as well as a dual-LED flash.