Are there alternative methods, besides IP addresses and cookies, that PHP developers can use to keep users logged in across multiple pages on a website?

One alternative method that PHP developers can use to keep users logged in across multiple pages on a website is by using sessions. Sessions store user information on the server side and provide a unique session ID to the client, which can be used to retrieve the user's data across pages. This method is more secure than using cookies, as the data is stored on the server rather than the client's browser.

// Start the session
session_start();

// Set user information in the session
$_SESSION['user_id'] = $user_id;
$_SESSION['username'] = $username;

// Retrieve user information from the session
$user_id = $_SESSION['user_id'];
$username = $_SESSION['username'];