We're now ready to enhance our Flask ToDo application by adding user registration functionality. In the previous lesson, we laid the groundwork with the authentication middleware. Now, let's take it a step further and allow users to sign up and create accounts.

The user registration process is crucial for letting new users onboard into our application. It safely stores their credentials and prepares them for future logins. By the end of this lesson, we'll collectively integrate user registration into our Flask app using models, services, and controllers.

Let's start by creating the file for our User model, which will store user-related data. We'll head over to app/models/ and create a new file named user.py.

Let's break it down:

• Data Storage: Our User model is a representation of the user data structure. It includes an id for unique user identification, a username which is set to be unique and required, and a password_hash that stores the user's password securely in a hashed format.
• Security: With generate_password_hash, we convert plain text passwords into hashed passwords, which are more secure and protect user credentials from being easily read in case of a database breach.

Hashing involves transforming data, such as passwords, into a fixed-size string of characters—a hash code. This method enhances security by storing the hash instead of the plain text version, making it significantly more challenging for attackers to retrieve the original data.

Werkzeug is a Python library that simplifies web development by offering various utilities, including secure password hashing. It employs the PBKDF2 algorithm, which uses salting and multiple iterations to create strong hashes resistant to attacks.

To incorporate Werkzeug in your Flask app, you can install it with the following command:

Next, we'll create a service to handle the user registration logic. In app/services/, let's create a file named user_service.py with the following code:

Here's what this does:

• User Existence: The service first checks if there's an existing user with the same username in the database. This prevents duplicate registrations and ensures each username is unique.
• Registration Process: If no user exists with the provided username, a new User instance is created. The password is hashed and securely stored, and the new user object is added to the database and committed as a transaction. This returns the new user if registration is successful.

Now let's move on to the user_controller. The controller file was already set up in our last lesson, so we'll just expand it to include the new registration route.

Here's what we did:

• Form Handling: The register route processes form input for username and password, passing them to the registration service.
• Feedback: Using Flask's flash function, we notify users about the success or failure of their registration. If registration is successful, the user is prompted to log in; if not, they're informed that the username is already taken.

After adding the registration route in the controller, it's important to update our authentication middleware to make sure users can access this route without needing to be logged in. We do this by ensuring the route is included in the accessible endpoints.

In app/middlewares/authentication_middleware.py, we need to add 'user.register' to the list of open routes:

By listing 'user.register' here, we allow users to access the registration page without being logged in, ensuring a seamless registration process.

Finally, in the auth.html template, we'll add flash messages and define an action for the register button to improve user feedback and interactions:

Here's what we've done:

• Flash Messages: We integrated flash message display to keep users informed about their actions' results, such as registration success or conflict.
• Register Button Action: The register button is configured with a formaction that directs form submissions specifically to the user.register route, separating the registration logic from login.

Together, we've integrated user registration into our Flask ToDo application. Here's what we've accomplished:

• We created and explored the User model for secure storage.
• We implemented the UserService class for registration logic.
• We expanded the user_controller with a new registration route.
• We updated the authentication middleware to include the registration route, ensuring users can access it without being logged in.
• We enhanced the auth.html template to integrate flash messages for user feedback and set up the registration button to route correctly.

As you proceed to the hands-on practice exercises, you'll reinforce and apply these concepts to strengthen your understanding. Well done on reaching this milestone!