How to attribute sales to any source via querystring (UTC)

[JaydenLNext]

I'd like to attribute a sale to any source, and see it in reporting stats. How?

Blows my mind that this basic need has not been solved by one of the world's most used services (unless I'm wrong. Shopify support just told me they had no idea how to do it).

This person seems to have achieved it in Shopify, and wrote the following on BigCommerce's forums:

"On Shopify, to track orders made through a referral link, I can send a customer to a store with a specific query param in the URL. I then set this query param as a hidden cart attribute. If an order is made, this attribute will appear in the order information and I can track the source of the conversion event."

I'd be happy to do it this way as a bare-bones method to at least begin source attribution. I do not want to use a third-party app.

So, how do you use a querystring parameter to set a hidden cart attribute?

And/or - is there a better way?

[Metz]

Following this post as I would love to know this, too. It is an issue I have been trying to solve for a friend's store, without success.