Starting today, you'll be able to log into some Google services from your phone with nothing more than your fingerprint (or another screen unlock method). Although Android got support for FIDO2 earlier this year, Google is now allowing some of its services to take advantage of the protocol's password-less authentication, starting today with Pixel devices, and rolling out over the next few days more widely to other devices running Android 7 Nougat and later.
If you aren't familiar with FIDO2, the very short version is that it's a two-factor authentication method that means you won't need to use a password to log into supported services. It's still secure, there's an implied lineage of authentication history (associated devices are "Bootstrapped" as Google calls it), it's just a whole lot more convenient than typing your password.
The different building blocks which contributed to Google's announcement today have been rolling together for some time. Last year Chrome for Android picked up the Web Authentication API and CTAP support, and later snagged fingerprint-based authentication. With this new system, logging into services — both Google's and those from other companies — can be as easy as a tap on a fingerprint reader. And if you're worried about having your fingerprint sent who knows where online, don't be. The authentication happens on-device, only a key demonstrating the validity of your fingerprint is sent online.
We don't know which individual Google services are and aren't compatible with this new login method just yet, but we have tested it with Google's published example, passwords.google.com, and it works as described. Rather than being asked for login credentials like username and password, the site can authenticate those details based on information stored on-device, requiring just a tap of your digit to a fingerprint reader (or your lockscreen authentication details) to log in.
Testing the feature on a Pixel 3a running Android Q DP6. Note that if you don't have a fingerprint associated, it still works via screen lock.
To use the feature, Google notes that you'll need a phone running Android 7 Nougat or later, your phone will need to be logged in to your Google account, and you'll have to have screen lock set up. (Though the feature is only working on Pixels at the time of writing, it will roll out to other phones in the next couple of days.) The full list of authentication options is here. A fingerprint isn't a hard requirement, but it is a lot easier than tapping out a PIN/password or pattern.