I try to implement sign up AWS Mobile Hub process in an iOS app. I chose "How are your users going to login?" only email option. But the test app (downloaded from 'Integration Steps' page after User pool creation) have required Username field on a sign-up and log-in screens. Can I implement this flow with user email and password fields only?
It should be possible, though you might have to autogenerate a fake username on the first sign up. You should make sure email is then passed in as an attribute and is set as an alias for the pool.
One possible sticking point: if email and phone are both given to be confirmed, phone overrides email. In that case, you'd have to ensure manually that emails are confirmed.