The feature was revealed via Safari’s beta release notes. In a video for web devs, the company explains the way this is implemented. To put it really simply, it works similarly to the way Face ID and Touch ID already works in iOS. When you first log into your apps, you enter your password, then you can use biometrics for subsequent logins.
This makes for a simpler and safer login process. This will be especially the case when visiting sites or services that require frequent sign ins, especially after inactivity periods. Banking websites come to mind, especially those without dedicated apps of their own. Apple is naturally asking web developers to test the feature out, so that it can roll out alongside Safari 14. The browser, as mentioned, is scheduled to be released alongside iOS 14, iPadOS 14, and macOS Big Sur, all of which are scheduled to be publicly available in fall. (Source: Apple [1], [2] via AppleInsider)
