Portal - User/Customer web form

Hi everyone,

I’m looking for a solution to create a web form that is accessible from the portal in order to allow my customer to login and fillup it. I want this form to be attached (linked) to my related customer doctype.
I can have the userId from the frappe JS object but I don’t know how to make this new document linked to the customer doctype.
Any help or advise will be more than welcome. Ideally I’m looking for a solution that don’t involve custom app :wink: