Google Smart Lock app on the iOS has received a new update that allows you to use you iPhone as physical two-factor authentication (2FA) security key. With version 1.6, you can set your phone's built-in security key for your Google Account. As The Verge notes, once you set up your iPhone, attempting to log into a Google service on a different device will send a push notification to the nearby iPhone. Once you authenticate, the login process is completed on the other device. This feature had been already available for Android phone owners.