How can PHP prevent multiple logins with the same account while handling user logout status?

To prevent multiple logins with the same account while handling user logout status, we can store a unique session identifier in the user's account table in the database. When a user logs in, we can check if the session identifier matches the one stored in the database. If it does not match, we can invalidate the session and log the user out.

// Check if session identifier matches the one stored in the database
if ($_SESSION['session_id'] !== $user['session_id']) {
    // Invalidate session and log user out
    session_unset();
    session_destroy();
    header("Location: logout.php");
    exit;
}