Promo/discount code in URL

Hi,

I'd like to have an embedded discount code and User ID to track the users and discounts of people who were referred by a partner/referral website.

Something like: 

https://store.com/products/our-best-product?referral=[DISCOUNT]&cdata=[CUSTID]

I've looked for some info in the help guides but could not find anything. 

Thanks in advance for your help

Brice