Firebase Twitch OAuth Flow (Cloud Functions implementation)

index.js

'use strict';

const functions = require('firebase-functions');
const admin = require('firebase-admin');
const cookieParser = require('cookie-parser');
const crypto = require('crypto');
const { AuthorizationCode } = require('simple-oauth2');
const fetch = require('node-fetch');

// Firebase Setup
const admin = require('firebase-admin');
// @ts-ignore
const serviceAccount = require('./service-account.json');
admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
  databaseURL: `https://${process.env.GCLOUD_PROJECT}.firebaseio.com`,
});

const OAUTH_REDIRECT_URI = `https://${process.env.GCLOUD_PROJECT}.firebaseapp.com/popup.html`;;
const OAUTH_SCOPES = 'user:read:email';

/**
 * 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://id.twitch.tv',
      tokenPath: '/oauth2/token',
      authorizePath: '/oauth2/authorize',
    },
    options: {
      bodyFormat: 'json',
      authorizationMethod: 'body',
    },
  };
  return new AuthorizationCode(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 authorizationCode = twitchOAuth2Client();

  cookieParser()(req, res, () => {
    const state = req.cookies.__session || crypto.randomBytes(20).toString('hex');
    console.log('Setting verification state:', state);
    res.cookie('__session', state.toString(), { maxAge: 3600000, httpOnly: true });
    const redirectUri = 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 authorizationCode = twitchOAuth2Client();

  try {
    cookieParser()(req, res, async () => {
      try {
        console.log('Received verification state:', req.cookies.__session);
        console.log('Received state:', req.query.state);
        if (!req.cookies.__session) {
          throw new Error(
            'State cookie not set or expired. Maybe you took too long to authorize. Please try again.'
          );
        } else if (req.cookies.__session !== req.query.state) {
          throw new Error('State validation failed');
        }
      } catch (error) {
        return res.jsonp({ error: error.toString() });
      }

      let accessToken;
      try {
        console.log('Received auth code:', req.query.code);
        const options = {
          client_id: functions.config().twitch.client_id,
          client_secret: functions.config().twitch.client_secret,
          code: req.query.code,
          grant_type: 'authorization_code',
          redirect_uri: OAUTH_REDIRECT_URI,
        };
        console.log('Asking token with options', JSON.stringify(options));
        accessToken = await authorizationCode.getToken(options);
        console.log('Auth code exchange result received');

        const twitchUser = await getTwitchUser(accessToken.toJSON().access_token);

        // Create a Firebase account and get the Custom Auth Token.
        const firebaseToken = await createFirebaseAccount(twitchUser);

        // Serve an HTML page that signs the user in and updates the user profile.
        return res.jsonp({ token: firebaseToken });
      } catch (error) {
        return res.jsonp({ error: error.toString() });
      }
    });
  } 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.
 *
 * @returns {Promise<string>} The Firebase custom auth token in a promise.
 */
async function createFirebaseAccount(twitchUser) {
  // The UID we'll assign to the user.
  const uid = `twitch:${twitchUser.id}`;

  // Save the access token to the Firebase Database.
  const db = admin.firestore();
  const databaseTask = db.collection('users').doc(uid).set(twitchUser);

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

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

async function getTwitchUser(accessToken) {
  console.log('Fetching Twitch user with access_token', accessToken);
  try {
    const response = await fetch('https://api.twitch.tv/helix/users', {
      method: 'GET',
      headers: {
        'Client-Id': functions.config().twitch.client_id,
        Authorization: 'Bearer ' + accessToken,
      },
    });
    const data = await response.json();
    return { ...data.data[0], access_token: accessToken };
  } catch (error) {
    console.error(error);
  }
}

I can't find it in my code anymore, I think I switched to the full redirect flow for some reason.