Auth0 Guardian

Auth0's Guardian Authenticator provides frictionless multifactor authentication. Just receive a push notification, approve it, and you're logged in! It's multifactor made simple.

Note for developers: Guardian Authenticator is one of several multifactor options that can be used with the Auth0 identity platform (https://auth0.com). Enabling it is as simple as toggling a single switch, and it supports SMS-based authentication as well. With Guardian Authenticator and Auth0, you don't have to change your apps to support the latest in multifactor authentication.