What are the best practices for handling session expiration and user authentication in PHP?

Session expiration and user authentication are crucial aspects of web application security. To handle session expiration, it is important to set a reasonable session timeout period and implement a mechanism to check and renew the session before it expires. For user authentication, always validate user credentials securely and store sensitive information like passwords hashed and salted.

// Set session timeout period to 30 minutes
ini_set('session.gc_maxlifetime', 1800);

// Start or resume a session
session_start();

// Check if the session is about to expire and renew it if necessary
if (isset($_SESSION['LAST_ACTIVITY']) && (time() - $_SESSION['LAST_ACTIVITY'] > 1800)) {
    session_regenerate_id(true);
    $_SESSION['LAST_ACTIVITY'] = time();
}

// User authentication example
$username = "example_user";
$password = "example_password";

// Validate user credentials securely
if ($_POST['username'] == $username && $_POST['password'] == $password) {
    // User authentication successful
    $_SESSION['authenticated'] = true;
} else {
    // User authentication failed
    $_SESSION['authenticated'] = false;
}