Describe the login process in a system.

1. The user enters login credentials (username and password) on the login page.
2. The browser sends an HTTP POST request to the server with the entered data.
3. The server receives the request and passes the credentials to the authentication component.
4. The authentication component compares the received data with the information in the user database:
   • Checks for the existence of a user with such a login.
   • Hashes the entered password and compares it with the stored password hash for that user.
5. In case of successful authentication:
   • The server creates a session for the user or generates an access token (e.g., JWT).
   • The session/token is associated with the user's unique identifier and contains information about their access rights.
   • The server sends an HTTP response with a 200 OK status and transmits the session (via cookie) or access token to the user's browser.
   • The browser saves the cookie or token.
   • The user is redirected to the main or target page.
6. In case of failed authentication (incorrect login or password):
   • The server sends an HTTP response with an error code (e.g., 401 Unauthorized) and an error message.
   • The browser displays an error message to the user on the login page.
7. For subsequent requests to protected resources, the browser automatically sends the saved session (cookie) or access token in the HTTP request headers.
8. The server verifies the validity of the session/token and grants access to the resource if authentication is confirmed and the user has the necessary rights.

Example (pseudocode):

# On the server
def login(username, password):
    user = database.find_user(username)
    if user and hash(password) == user.hashed_password:
        session_id = generate_session_id(user.id)
        database.save_session(session_id, user.id)
        return {"status": "success", "session_id": session_id}
    else:
        return {"status": "fail", "message": "Invalid credentials"}

# On the client (in the browser)
async function handle_login_submit(event):
    event.preventDefault();
    const username = document.getElementById("username").value;
    const password = document.getElementById("password").value;

    const response = await fetch("/api/login", {
        method: "POST",
        headers: {
            "Content-Type": "application/json"
        },
        body: JSON.stringify({ username, password })
    });

    const data = await response.json();
    if (data.status === "success") {
        // The server will set a cookie with session_id, or we can save the token from the response
        window.location.href = "/dashboard";
    } else {
        alert(data.message);
    }