It looks like Apple is trying out new ways for users to sign onto iCloud.com. Apple users who have the beta versions of iOS 13, iPadOS 13, and macOS Catalina can use Face ID or Touch ID to sign in. Beta users who visit beta.icloud.com or beta-equipped devices will get asked via a popup if they want to sign using either one of those systems. They won’t need two-factor authentication after. This move makes sense as these methods are already being used to unlock devices and make purchases with Apple Pay. And if it’s secure enough for those, it should be secure enough for iCloud.
Source: The Verge