You can find the sample project for this chapter here: https://github.com/mikerworks/packt-lean-onboarding.
The code sample has been updated, so it will use the latest and greatest (at the time of writing). Digits, the Fabric phone authentication service, has been replaced by the Firebase phone authentication service. The code sample is now using this service and, while I was busy anyway, I have converted the Android Java example to Kotlin.
You can have a look at the app first, or if you want to configure it for your own use you need to configure Fabric and Firebase first.
Visit https://fabric.io and create an account. Once you have done that and have confirmed it, you can proceed. Enter a team name (for example packt-demo) and choose a platform (Android). After that, a new page in the wizard will show a number of options. Pick the Twitter option first. The first...