Welcome to this lesson on Session-Based Authentication in C++. In the previous lesson, we explored API authentication using API keys, focusing on how these keys serve as a passcode for accessing protected endpoints. Now, we will delve into session-based authentication, a method wherein the server keeps user session information, providing a stateful experience. Unlike the stateless API keys, session-based authentication offers a user-friendly way to manage active sessions, track user interactions, and facilitate resource access. By the end of this lesson, you will be able to sign up, log in, access protected resources, and log out using session-based authentication in C++.

Session-based authentication enables users to maintain a logged-in status as they interact with different endpoints in an application. In stateless authentication (such as API keys), every request must contain the necessary credentials, and the server does not retain any information about previous interactions. In contrast, session-based authentication creates and maintains state between requests. This means that once a user logs in, the server assigns a session ID, which the client must include in subsequent requests. The session ID acts as a temporary authentication token, allowing users to stay logged in without re-entering credentials.

Cookies are small pieces of data stored on the client side and sent to the server with each request. In session-based authentication, the server typically returns a Set-Cookie header containing a session ID when a user logs in. This header instructs the client to store the session ID as a cookie and send it back in subsequent requests. The C++ client, using a library like cpp-httplib, can interact with a RESTful API by maintaining user session information on the server, thus creating a stateful experience.

During login with your C++ client:

• Session Creation: A POST request with your username and password creates a unique session ID, often returned in a "cookie."
• Ongoing Requests: Your C++ client must include this session ID in subsequent requests, so the server recognizes the session without requiring credentials to be re-entered.
• Session Termination: Sending a logout request invalidates the session on the server, ensuring that future requests using the old session ID are not accepted, thus safeguarding your session integrity.

In C++, you can manage sessions and cookies using libraries like cpp-httplib. This involves manually handling cookies and session data for interaction with RESTful API endpoints while maintaining user state securely.

Before diving into the authentication steps, it's important to understand session management using C++ libraries like cpp-httplib. This library helps create and manage HTTP requests. Here's how you can establish a session:

Why Use cpp-httplib for Sessions?

• Stateful Interactions: You need to manage cookies manually. After login, store the session ID from the server to use it in subsequent requests.
• Efficiency: cpp-httplib allows efficient connections and helps maintain the state across multiple requests.
• Consistency: By storing the session ID, you ensure that all requests maintain consistent authorization across your session's lifespan.

Managing session data manually is crucial in C++ for effective session-based authentication. Let’s proceed to the practical steps of implementing this using cpp-httplib.

Creating a user account starts by sending a POST request to the API’s signup endpoint. Here's how you can do it using C++:

In this example, a POST request with a username and password is sent to /auth/signup to create a user account. 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 action is logging in. This involves posting login credentials and managing the session ID. Here's how it is handled in C++:

Here, a POST request is sent to /auth/login, using the session ID from the cookies to maintain an active session. 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, you can access protected API endpoints using the session ID. Here is a C++ example:

This example sends a GET request to /todos using the session ID for authentication. 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 a session, send a POST request to log out. Here's how it's done with C++:

A POST request to /auth/logout effectively terminates the session. 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:

The practice server you'll be working with implements a robust session invalidation mechanism. When handling the logout process, it first checks whether the user is authenticated. If so, it immediately adds the existing session ID to a set of invalidated sessions, making sure the server no longer accepts that session ID for future requests—even if it would normally remain valid until its expiration. Next, user session data is cleared, and the session cookie is set to expire, preventing any browser-based reuse of that session.

This implementation is crucial for understanding how session invalidation works in practice. While working on the exercises, you'll interact with this server that maintains a set of invalidated sessions, allowing you to experience firsthand how session IDs become unusable after logout. However, in real-world scenarios—especially with programmatic API interactions—if a session ID is not explicitly invalidated like our practice server does, it might remain valid until its set expiration time. This means a user could remain effectively logged in through automated scripts or other clients, even though they have "logged out" elsewhere. By proactively listing session IDs as invalid, you enforce an immediate cutoff on the server side, preventing any further use of those IDs to access protected endpoints.

After logging out, attempts to access protected endpoints with the old session ID will fail:

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 explored the process of session-based authentication in C++, covering signing up, logging in, accessing secure resources, and logging out. Managing an active session helps maintain effective and secure user states during API interaction. The upcoming exercises will reinforce your understanding and mastery of session-based authentication, equipping you for future lessons on advanced authentication techniques like JSON Web Tokens (JWT). Proceed with confidence to practice implementing these methods using C++.