Welcome to this lesson on Session-Based Authentication. In the previous lesson, we delved into API authentication using API keys, focusing on how these keys act as a passcode for gaining access to protected endpoints. Here, we take a step further and explore session-based authentication, a method where the server maintains user session information, providing a stateful experience. Unlike API keys, which are stateless, session-based authentication provides a user-friendly way to manage active sessions, track user interactions, and facilitate access to resources. By the end of this lesson, you will be capable of signing up, logging in, accessing protected resources, and logging out using session-based authentication.

Session-based authentication is a process that allows users to stay logged into a system as they interact with different endpoints in an application. Whether you are using a web browser or a client like a Dart script to interact with a RESTful API, session-based authentication involves maintaining user session information on the server, creating a stateful experience.

When you log in to a RESTful API using your Dart client, the server starts a "session" for you. This session is like a temporary ID card that validates your identity during your interactions with the API. A critical part of this process involves a "cookie," which is a small piece of data sent from the server and stored by your client.

In the context of a Dart-based client:

• Session Creation: After logging in by sending a POST request with your username and password, the server creates a unique session ID, often returned in a cookie.
• Ongoing Requests: Your Dart client, using the http package, can manually include this session ID in subsequent requests to the API. This allows the server to recognize the session without needing to re-enter your credentials.
• Session Termination: When your client logs out by sending a logout request, the server invalidates the session, stopping further requests with the old session ID from succeeding, safeguarding your session integrity.

By using Dart's http package, you can manage cookies and session data manually, enabling effective interaction with RESTful API endpoints while maintaining user state securely.

When working with session-based authentication in Dart, leveraging the http.Client object is advantageous for managing multiple requests efficiently. Here's why using a Client object is beneficial:

Why Use http.Client?

• Persistent Connections: The Client object maintains persistent connections, allowing you to reuse the same connection for multiple requests. This reduces the overhead of establishing new connections for each request, enhancing performance and efficiency.
• Cookie Management: Unlike browsers that automatically handle cookies, Dart's http package requires manual cookie management. The Client object provides a consistent context where you can extract cookies from response headers and include them in subsequent request headers.
• Resource Management: Using a single Client instance helps manage resources efficiently. When you're done with all requests, you can close the client with client.close() to release resources properly.

Using a Client object is particularly useful when implementing session-based authentication. It allows you to perform all authentication steps — signing up, logging in, accessing resources, and logging out — within a persistent connection context, ensuring better performance while you manually handle the session cookies across your API requests.

Before you begin the authentication process, you need to set up the base URL for the API, define the signup details, and create a client to manage the session. Here's how you can do it:

In the first step of session-based authentication, you need to create a user account. This action is performed by sending a POST request to the API's signup endpoint. Below is the code example showing how this can be accomplished:

In this example, a user account is created by submitting a POST request to the /auth/signup endpoint, along with a username and password. If the request is successful, a confirmation message and the server's response are displayed; otherwise, error details are provided. Upon successful signup, you would see the following output, confirming that the account has been created:

After signing up, the next step is to log in and initiate a session. This involves posting login credentials to an authentication endpoint. Here's an example of how this is implemented:

In this code snippet, after signing up, you proceed to log in via a POST request to /auth/login, re-using the client object to keep the session active. Successful login messages are shown if the credentials are accepted and the session is active, and the session ID is printed; otherwise, error details are displayed. Successful login results in the following output:

With an active session established, you can use your client object to make requests to protected endpoints of the API. Here's an example of how to achieve this using the sessionId:

Here, a GET request is used to access the /todos endpoint, assuming it's protected and requires an active session. The sessionId is included in the request headers to authenticate the session. When access is granted, it indicates that your session is valid and active; otherwise, error responses are provided in case of a failure. Accessing the protected resource successfully will produce the following output:

To end the session and log out by targeting the /auth/logout endpoint, ensuring that the session is cleanly terminated, you can use the following with the sessionId:

To log out, a POST request is made to /auth/logout, notifying the server to terminate the session. The sessionId is included in the request headers to ensure the correct session is terminated. A successful logout message is displayed upon completion; otherwise, error responses are provided if the request fails. After logging out, you will see the following message as confirmation:

After ending the session and logging out, any attempt to access protected endpoints without logging back in will fail. This is because the session is no longer active, and the server won't recognize your session ID. Here’s the output you can expect when trying to access a protected endpoint after logging out:

In this lesson, we journeyed through the process of session-based authentication, covering signing up, logging in, accessing secure resources, and logging out. By maintaining an active session, you have learned to manage user states effectively and securely — an important aspect of API interaction. As you transition to the practice exercises, these methods will form the backbone of your hands-on experience in securing endpoints. The upcoming practices are designed to reinforce your understanding and mastery of session-based authentication, preparing you for subsequent lessons that explore even more advanced methods like JSON Web Tokens (JWT). Dive into these exercises with confidence, applying what you've learned in a practical, results-oriented way.