Apple is trying out a new sign-in process for iCloud on the web for their next OS update (iOS 13, iPadOS 13, and macOS Catalina beta testers). When you head to beta.icloud.com on a device running the betas, you can now sign-in to your account using Face ID or Touch ID. Attempting to visit the regular iCloud.com while using a beta version of the operating systems will also automatically redirects to the beta iCloud site.

read more at https://appleinsider.com/articles/19/07/08/apple-trials-face-id-touch-id-logins-for-icloud-on-the-web