Firebase Cloud Functions Authentication Trigger Writes to Firestore

index.js

const functions = require('firebase-functions')
const admin = require('firebase-admin')
admin.initializeApp(functions.config().firebase)

const userRef = admin.firestore().collection('users')

exports.createUserAccount = functions.auth.user().onCreate(event => {
  const uid = event.data.uid
  const email = event.data.email
  const photoUrl =
    event.data.photoURL ||
    'https://pbs.twimg.com/profile_images/961651411363643392/DEsDYpZ8_400x400.jpg'
  return userRef.doc(uid).set({
    photoURL: photoUrl,
    email: email
  })
})