Passing Infu Contact ID from a web app to Infu Order Form

We have developed an industry-specific web app and are using the Infu REST API to move data between our app and Infu. Have just successfully subscribed to the REST Hooks to monitor infu orders.

We are using the Infu ContacID within our app as our unique “ownerid” .

I want to be able to have the app owner - after login to my app - click a link to “buy some more stuff…” and redirect the “owner” to infu order form(s) - one of 5 possible order forms.

I want to be able to pass my ownerid - which is the Infu contact id - to infu so that Infu knows who is ordering and the order form(s) know who it is - without asking.

Any advice/direction from anyone on how to accomplish this?