Sessions & Cookies

Session-based authentication is a traditional, stateful method for managing user identity in web applications. The process begins when a user logs in with their credentials. If the credentials are valid, the server creates a 'session'—a data structure that stores information about the logged-in user—and saves it on the server-side, often in memory, a cache, or a database. The server then generates a unique Session ID for this session. This Session ID is sent back to the client's browser and stored in a cookie. A cookie is a small piece of data that a server sends to the user's web browser. The browser stores it and sends it back with every subsequent request to the same server. On every following request from the user, the browser automatically includes the cookie with the Session ID. The server receives the request, extracts the Session ID from the cookie, looks up the corresponding session data in its storage, and thus identifies the user. This approach is 'stateful' because the server has to maintain the state (the session data) for every active user. While straightforward to implement, this can pose scalability challenges, as the session store can become a bottleneck and needs to be shared across all servers in a distributed system. It's important to configure cookies securely, using flags like `HttpOnly` to prevent access from client-side scripts and `Secure` to ensure they are only sent over HTTPS.