I have a cart products page, if a person clicks on a product add to cart button they will be redirected to the login page.
After a successful login, I need to send the user back to same products page.
A simple solution would be to store the "return" URL in a session variable before you kick to the login page. The login page would check for the presence of the session variable and then unset it prior to using a header location re-direct to return the user to the URL in question.
For example on the login page you'd use:
// Successfully logged in... $destURL = $_SESSION['kickurl'] ? $_SESSION['kickurl'] : '/index.php'; unset($_SESSION['kickurl']); header('Location: ' . $destURL); exit();