This post was originally published on our Technical Director's personal blog.

Amazon's cloud offering, AWS, provides a wealth of resources for developers and infrastructure engineers. In this article, I'll show how Amazon Cognito can be used to record user preferences and data without having to set up a server or database. I'll build a small React Native application which allows a user to log in with Facebook and save some data to the cloud for later retrieval.

Facebook Login

Prerequisites:

• Install npm and CocoaPods if you don't have them already
• Install React Native
• Create a new Facebook iOS app in the developer centre

Let's start by creating our React Native project and entering the project directory:

react-native init FacebookAwsReactNative
cd FacebookAwsReactNative

Let's install the Facebook React Native SDK via npm, that'll give us a nice login button for free:

npm install --save react-native-fbsdkcore react-native-fbsdklogin

We need to install some native code to make this work, so let's do that with CocoaPods. First we create a Podfile:

cd ios
pod init

Edit the file which was just created at FacebookAwsReactNative/ios/Podfile and add the following:

source 'https://github.com/CocoaPods/Specs.git'
pod 'React', :subspecs => ['Core', 'RCTImage', 'RCTNetwork', 'RCTText', 'RCTWebSocket'], :path => '../node_modules/react-native'
pod 'react-native-fbsdkcore', :path => '../node_modules/react-native-fbsdkcore'
pod 'react-native-fbsdklogin', :path => '../node_modules/react-native-fbsdklogin'
pod 'react-native-fbsdkshare', :path => '../node_modules/react-native-fbsdkshare'

You may need to perform some other steps here, as per the Facebook documentation. Go and have a read of that section just in case. Let's install the pods and then we'll have to faff around in Xcode for a bit.

pod install
open FacebookAwsReactNative.xcworkspace

Notice that we now use the xcworkspace file rather than the xcodeproj file; this is required for CocoaPods to do its thing.

Xcode Is Quite Horrible Really

Expand the FacebookAwsReactNative > Libraries folder and select all of the items in there and delete the references to them. This is because we've opted to use CocoaPods for React Native (see the pod 'React' line we added to the Podfile) so the items in Libraries are duplicates.

Let's move on to configuring the Facebook SDK. Open up info.plist using Open As > Source Code, and add the follow inside the root <dict> node:

<key>CFBundleURLTypes</key>
<array>
  <dict>
    <key>CFBundleURLSchemes</key>
    <array>
      <string>fb{your-app-id}</string>
    </array>
  </dict>
</array>
<key>FacebookAppID</key>
<string>{your-app-id}</string>
<key>FacebookDisplayName</key>
<string>{your-app-name}</string>

Next, open AppDelegate.m and add a new import:

#import <FBSDKCoreKit/FBSDKCoreKit.h>

Connect our AppDelegate to the FBSDKApplicationDelegate by adding the following to didFinishLaunchingWithOptions:

[[FBSDKApplicationDelegate sharedInstance] application:application
    didFinishLaunchingWithOptions:launchOptions];

And finally, add a method to allow us to navigate back to our app from Facebook:

- (BOOL)application:(UIApplication *)application openURL:(NSURL *)url sourceApplication:(NSString *)sourceApplication annotation:(id)annotation {
  return [[FBSDKApplicationDelegate sharedInstance] application:application
    openURL:url
    sourceApplication:sourceApplication
    annotation:annotation
  ];
}

Wonderful. Run the project and get your simulator running because we're now ready to add our login button.

Push The Button

We need to import the button component, and at the same time we'll import another class that we'll use later. Add the following:

import { FBSDKAccessToken } from 'react-native-fbsdkcore';
import { FBSDKLoginButton } from 'react-native-fbsdklogin';

Delete all of the default stuff inside the <View> component and replace it with the button code:

<FBSDKLoginButton
    onLoginFinished={this.onLoginFinished}
    onLogoutFinished={this.onLogoutFinished=}
    readPermissions={[]}
    publishPermissions={['publish_actions']}/>

We now need to add onLoginFinished and onLogoutFinished methods to our FacebookAwsReactNative class.

onLogoutFinished() {
    alert('Logged out.');
}

Simple!

onLoginFinished(error, result) {
    if (error) {
        alert('Error logging in.');
    } else {
        if (result.isCancelled) {
            alert('Login cancelled.');
        } else {
            alert('Login success!');
        }
    }
}

Less simple, but pretty self-explanatory. At this point, you should be able to run the app and login via Facebook, with the various alert messages firing as appropriate.

But we want to take one more step; we want to be able to link this login to persistent data stored on Amazon Cognito. This needs two steps: firstly to get a unique token to identify the Facebook login, and secondly, to sync local data up to Cognito. Fortunately this becomes super-easy thanks to the Amazon SDK and the React Native Cognito project.

First, we need to get an access token from Facebook to use as a link between FB and Cognito. FBSDKAccessToken.getCurrentAccessToken takes a single callback argument which is passed the token we need. We then need to install (follow the instructions) and import React Native Cognito. Add this along with your other import statements:

import Cognito from 'react-native-cognito';

Next, we initialise the credentials for Cognito and sync up some data!

FBSDKAccessToken.getCurrentAccessToken((token) => {
    if (token) {
        Cognito.initCredentialsProvider(
            awsIdentityPoolId,
            token.tokenString,
            awsRegion);

        Cognito.syncData('testDataset', 'key', 'value', (err) => {
            // success!
        });
    }
});

You'll need to have created a Federated Identity Pool and set up Facebook as an Authentication Provider. Populate the awsIdentityPoolId and awsRegion variables accordingly and the above code can be run at any point after a successful login.

Visit the Identity Pool in the AWS Console and you'll see a dataset called "testDataset" with a single key/value entry.

This has been a whistlestop tour on moving to a serverless setup with Facebook logins and Amazon Cognito. The full code can be found on GitHub.