Model user actions through a rest services app


I am working in a web app that uses a rest services layer to interact with the business logic. So all user actions goes to a rest service that will then invoke in some way the process engine. Since userTasks looks to need a form, what would be the best way to model it? Using a receive task ,a manual task or something else? It is possible to create the form programatically from the java side and then pass it to the process engine?