The Firebase Auth Quickstart provides a great tutorial on how to add authentication to your application, but without two-factor authentication (2FA), it's a bit insecure! Adding an extra layer of security to your application is simple using the Nexmo Verify SDK. To complete this tutorial, you will need a Vonage API account and a virtual phone number. You can sign up for these on the Vonage website. The tutorial also uses OAuth providers like Google and Twitter. Once you have all the necessary credentials, you can add two-factor authentication to your application using the Nexmo Verify SDK. This allows you to allocate more time to developing your app by providing a managed UI solution that enables you to make verification requests securely and with ease.