- User can register buy using their email, username, and password.
- Email and username is unique in entire system, no users have same username of others, an email address is used in an account.
- User can log in by using username and password.
- User can stay loged in in 24 hours. (we don't want to overcomplicate this project by support Oauth).
- User can see all todos, including completed todos.
- User can add a new todo.
- User can update content of a todo or mark uncompleted todo to be completed.
- User can delete a todo.
- A completed todo item can only exist within 3 months, previous todos will be deleted from system.