Author has developed simple and basic authentication app for flutter, which is having login signup screen in flutter. Inspiration of app design is from Frank Arinze. There are three pages. first one is welcome page from which we can go on login or signup screen.
second is login and third one is signup screen. For demo purpose you can simply download the app.

Download App 

you can see in below image that how it is looking.

Screenshots

Credits:
this project is done by Sonu Sharma
and you can download this project from the below link
https://github.com/TheAlphamerc/flutter_login_signup/archive/master.zip
and can visit original source page from below link
https://github.com/TheAlphamerc/flutter_login_signup