How to implement the registration form

You display a registration form to the user, in which he can fill in his card data. All parameters are in hidden fields.
Template example :

Registration with 3d secure Authentication

Depending on the card used during the payment, the submission of the registration form, a 3DSecure authentication may be necessary.
In this case, the HTML page of the 3DSecure form is sent in response content with a http status code 200 (OK).
The submission of the 3DSecure form will end with a 302 redirection to the url entered in the urlReturn field of the initial request.