Hello,
I would like to propose that your app will be created using following:
- Bootstrap v3.2
- Rails 4.2
- Some gems for generate unique code (if necessary), encrypt password
Suppose that you will want to manage all inputed information, I will happy to create an simple admin panel for your monitoring (no need to use RailsAdmin to simplified the structure). From that, you can list, edit, remove all user and create unique PIN. And yes, there should be a sign in form, which derived from sign up form.
I will also do some css so that your sign up form look nicely on both computer browsers and mobile devices.
Please let me know if you have any more request
Best,