PayPal Auto Return with PrestaShop

Kim from Colillas Branding (whose English was so good that I was surprised to see he was Spanish) asked today how to get PayPal to return directly to the website instead of first showing a "confirm payment" page. Returning to the site insures that you have a chance to show your tracking code, as the extra step that PayPal puts in can keep that from happening.

I googled and found the PayPal Auto Return feature, which looked like exactly what I needed. However, the location described in the above link does not exist in my PayPal account (I needed to look under Profile -> Account Settings -> Selling Options -> Website Preferences).

There I could turn on Auto Return, but I couldn't find what the return URL should be set to. There are questions on the PrestaShop forum asking what the return URL needs to be, but no useful replies.

So, time to "use the force.... read the source". In the PayPal module (the official PrestaShop one from 1.6.1.2), they set PAYPAL_RETURN_LINK to /modules/paypal/paypal_login/paypal_login_token.php. I added my domain to the front of that (i.e. I set "Return URL" in PayPal to http://www.mysite.com/modules/paypal/paypal_login/paypal_login_token.php), and it works... I was immediately sent to my shop on payment, the order confirmation page was shown (I'll need to look for that template in the PayPal module and customize it... another item for my to do list), the Google Tag Manager code got called, and the order is marked as paid PrestaShop. Bingo.

Now if I only knew how to do the same with RedSys for my ING payments... Kim! Help!