REST API for completeTaskWithForm methods in TaskService

I’m looking into use the Flowable REST-API (latest 6.3.1) to complete tasks with forms defined in the form-engine. (Similar to what is used in the flowable-task app.)

I have looked in the documentation and source code and cannot find any REST APIs defined which can be used to complete a task with a form (TaskService#completeTaskWithForm(…)) or to retrieve the form for a task(TaskService#getTaskFormModel(…)).

Is there any way to perform this with the current REST API? I do not have to use the TaskService if there is some other way to achieve this.