Firebase authentication

As we have seen before, Firebase contains a collection of useful technologies and we need to configure each one that we might need for our project. Let's configure the authentication layer of our app. The authentication layer is fundamental for our app; if you remember, the user favor requests are made to friends, and for this to happen, we need the user to be capable of sending the request to a specific user. We do this identification by using the user's phone number as its identity. We need to do that in the following steps:

1. Add the Firebase auth plugin to the project
2. As pointed out before, we simply need to add the firebase_auth plugin dependency to our pubspec, as shown in the following code:

# part of pubspec.yaml
dependencies:
 ...
 firebase_core: 0.3.4 # Firebase Core 
 firebase_auth: 0.8.4+5 # Firebase Auth  // add this

3. Enable phone authentication...