How do I redirect from a jump page through user/register or user/login to a destination page inside drupal

I'm using Drake (Drupal/PHP) in this case, but my problem is still general.

I need to get my user from an outside jump page (showing their Flickr photos) to an internal drupal page. I need a valid $user->uid before I can import the Flickr photos into the user account. My problem is redirecting the user through Registration and/or Login before landing on the target page.

The following code successfully redirects the user through 'user/register' and then to the target $dest_url. But the redirect breaks if the user goes to the 'Login' tab. How do I fix that, or is there a better way to do this? Is there a page/module with both register and login on the SAME page?

function drake_authenticate($dest_url) {
        // drupal_set_message("drake_dispatcher,  dest=$dest_url");

	// By default, all drake pages are visible, 
	// but redirect the following pages through user/register
	$redirect_register_list = array('flickr/submit_order');
	
        // grab the last 2 parts of the $dest_url
	$target_parts = explode('/',$dest_url);
	$target = array_pop($target_parts);
	$target = array_pop($target_parts).'/'.$target;
	$result = in_array($target, $redirect_register_list);
	if (!$result) return;
	
	// redirect to user/register 
        global $user;
        if ($user->uid > 0) {
	   return;
        } else {
           drupal_set_message(t("Step 3 of 4. Please register or log in before importing your photos."));
           unset($_REQUEST['destination']);
           drupal_goto("user/register",drupal_get_destination());
        }
  print $output;
  exit();
}