Capture form parameters of request on gateway and add additional form parameters to it, then forward all parameters to the backend as request.
Example: If the gateway policy captured form parameters P1 and P2 from request, add P3 as form parameter to the request through policy and send response including parameters P1, P2 and P3 as request to the backend.
CA API Management Gateway (All versions)
Gateway does not have assertions that enables to manipulate FORM parameters inside gateway policy. So, to Add/Modify/Delete form parameters, we need to recompose the entire message.