Firebase Cloud Function 3rd Party Oauth Flow For The Web

index.js

const functions = require('firebase-functions');
var admin = require("firebase-admin");
const cookieParser = require('cookie-parser');
const crypto = require('crypto');

var serviceAccount = require("./service-account.json");
const APP_NAME = "twitch-playground";

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
  databaseURL: "https://twitch-playground.firebaseio.com"
});

const OAUTH_REDIRECT_URI = `https://localhost:5000/popup.html`;
const OAUTH_SCOPES = 'user_read';

/**
 * Creates a configured simple-oauth2 client for Twitch.
 */
function twitchOAuth2Client() {
  // Twitch OAuth 2 setup
  // TODO: Configure the `twitch.client_id` and `twitch.client_secret` Google Cloud environment variables.
  const credentials = {
    client: {
      id: functions.config().twitch.client_id,
      secret: functions.config().twitch.client_secret
    },
    auth: {
      tokenHost: 'https://api.twitch.tv/kraken/',
      tokenPath: '/oauth2/token'
    }
  };
  return require('simple-oauth2').create(credentials);
}

/**
 * Redirects the User to the Twitch authentication consent screen. Also the 'state' cookie is set for later state
 * verification.
 */
exports.redirect = functions.https.onRequest((req, res) => {
  const oauth2 = twitchOAuth2Client();

  cookieParser()(req, res, () => {
    const state = req.cookies.state || crypto.randomBytes(20).toString('hex');
    console.log('Setting verification state:', state);
    res.cookie('state', state.toString(), {maxAge: 3600000, secure: true, httpOnly: true});
    const redirectUri = oauth2.authorizationCode.authorizeURL({
      redirect_uri: OAUTH_REDIRECT_URI,
      scope: OAUTH_SCOPES,
      state: state
    });
    console.log('Redirecting to:', redirectUri);
    res.redirect(redirectUri);
  });
});

/**
 * Exchanges a given Twitch auth code passed in the 'code' URL query parameter for a Firebase auth token.
 * The request also needs to specify a 'state' query parameter which will be checked against the 'state' cookie.
 * The Firebase custom auth token, display name, photo URL and Twitch acces token are sent back in a JSONP callback
 * function with function name defined by the 'callback' query parameter.
 */
exports.token = functions.https.onRequest((req, res) => {
  const oauth2 = twitchOAuth2Client();

  try {
    cookieParser()(req, res, () => {
      console.log('Received verification state:', req.cookies.state);
      console.log('Received state:', req.query.state);
      if (!req.cookies.state) {
        throw new Error('State cookie not set or expired. Maybe you took too long to authorize. Please try again.');
      } else if (req.cookies.state !== req.query.state) {
        throw new Error('State validation failed');
      }
      console.log('Received auth code:', req.query.code);
      oauth2.authorizationCode.getToken({
        code: req.query.code,
        redirect_uri: OAUTH_REDIRECT_URI
      }).then(results => {
        console.log('Auth code exchange result received:', results);

        // We have an Twitch access token and the user identity now.
        const accessToken = results.access_token;
        const twitchUserID = 1;
        const profilePic = 'www.google.com';
        const userName = 'need to do';

        // Create a Firebase account and get the Custom Auth Token.
        createFirebaseAccount(twitchUserID, userName, profilePic, accessToken).then(firebaseToken => {
          // Serve an HTML page that signs the user in and updates the user profile.
          res.jsonp({token: firebaseToken});
        });
      });
    });
  } catch (error) {
    return res.jsonp({error: error.toString});
  }
});

/**
 * Creates a Firebase account with the given user profile and returns a custom auth token allowing
 * signing-in this account.
 * Also saves the accessToken to the datastore at /twitchAccessToken/$uid
 *
 * @returns {Promise<string>} The Firebase custom auth token in a promise.
 */
function createFirebaseAccount(twitchID, displayName, photoURL, accessToken) {
  // The UID we'll assign to the user.
  const uid = `twitch:${twitchID}`;

  // Save the access token tot he Firebase Realtime Database.
  const databaseTask = admin.database().ref(`/twitchAccessToken/${uid}`)
      .set(accessToken);

  // Create or update the user account.
  const userCreationTask = admin.auth().updateUser(uid, {
    displayName: displayName,
    photoURL: photoURL
  }).catch(error => {
    // If user does not exists we create it.
    if (error.code === 'auth/user-not-found') {
      return admin.auth().createUser({
        uid: uid,
        displayName: displayName,
        photoURL: photoURL
      });
    }
    throw error;
  });

  // Wait for all async task to complete then generate and return a custom auth token.
  return Promise.all([userCreationTask, databaseTask]).then(() => {
    // Create a Firebase custom auth token.
    return admin.auth().createCustomToken(uid).then((token) => {
      console.log('Created Custom token for UID "', uid, '" Token:', token);
      return token;
    });
  });
}