As a user, I want to be able to register for an account easily.

start with email for now, then implement others later.

with email: https://medium.com/flutterpub/flutter-how-to-do-user-login-with-firebase-a6af760b14d5

with google: https://pub.dev/packages/google_sign_in

with facebook: https://pub.dev/packages/flutter_facebook_login

with phone number: https://medium.com/@jackwong_60367/sms-code-authentication-in-flutter-23d5071e084b
or
https://medium.com/flutter-community/firebase-phone-authentication-on-a-flutter-app-78104686efc5