function logged_in() {
	if($_SESSION['authorized'] == true) {
		return true;
	} else {
		return false;
	}
	
}
function login_required() {
	if(logged_in()) {	
		return true;
	} else {
		header('Location: login.php');
	}
	
}

2 login functions that check if a user is logged in by checking is a session is equal to true that would have been set on login.

If not logged in the redirect to login.php

Login checker Functions

login

PHP