Populate workflow input form element values with REST call result

I'm developing a custom workflows for creating Services and Services group in one or more NSX because workflows for this are missing in the NSX plugin and I had to use HTTP-REST plugin.

What I achieved at the moment is:

• Create a Service
• Create a Service group

Now I want to add Services to a Service Group, so I need to call another REST Operation, and I would like to populate the input form elements with the already existing services and service groups, in this way I can show to the user a dual list element where the user can select the services from.

I'm not able to find a specific documentation for this as the docs found in VMWare portal are just showing very basic stuff.

Is it possible to populate form element values with the result of a REST call?

Thanks in advance.