[codorial] Add Google login

codorials/authentication-with-firebase/config.json

@@ -35,6 +35,10 @@
       "title": "Facebook Login",
       "file": "facebook-login"
     },
+    {
+      "title": "Google Login",
+      "file": "google-login"
+    },
     {
       "title": "Conclusion",
       "file": "conclusion"

codorials/authentication-with-firebase/google-login.md

@@ -0,0 +1,45 @@
+# Google Login
+
+Much like Facebook loginin, Firebase provides the ability to accept and sign in with a Google credential.
+
+## Installing `react-native-google-signin`
+
+To sign in with Google, we recommend using `react-native-google-signin`. This provides a native way of obtaining the users
+Google accounts and their required `accessToken`.
+
+```
+npm install react-native-google-signin --save
+react-native link react-native-google-signin
+```
+
+## Creating a credential
+
+To generate a new credential for the user, simply call the asynchronous `signIn` method `react-native-google-signin` provides and create a new
+credential from the `firebase.auth.GoogleAuthProvider`:
+
+
+```js
+import { GoogleSignin } from 'react-native-google-signin';
+
+// Calling this function will open Google for login.
+export const googleLogin = async () => {
+  try {
+    // Add any configuration settings here:
+    await GoogleSignin.configure();
+
+    const data = await GoogleSignin.signIn();
+
+    // create a new firebase credential with the token
+    const credential = firebase.auth.GoogleAuthProvider.credential(data.idToken, data.accessToken)
+
+    // login with credential
+    const currentUser = await firebase.auth().signInAndRetrieveDataWithCredential(credential);
+
+  } catch (e) {
+    console.error(e);
+  }
+}
+```
+
+The flow here is exactly the same as the rest of our app; logging in with the newly created credential will trigger our `onAuthStateChanged` lister to fire with
+the new user, logging us into the application.