I've searched the docs, and can't find anything that might help... and can't imagine something like this hasn't come up before.
TL;DR - we want to set a contact attribute (maybe "OTHER LEAD SOURCE") to a value using a GET value upon first page-load.
This would be the workflow on the website:
A channel partner provides a lead with a URL, such as www.domain.com?other_lead_source=someguy
A JS script communicates with the API to associate that attribute with the visitor
From that point forward, before any forms are submitted, that attribute is retained via HS cookie
If the visitor submits an HS form, the contact is created, with the OTHER LEAD SOURCE column set to "someguy"
Then we set workflow rules to alert the appropriate channel partner manager to the new lead.
Is this possible?