Using Camunda instead of an actual application server

Hey good people,

Can you use Camunda as a contoler in a web app. (as in mvc architecture) ?
Is it a good idea?

No, you have to implement the controller yourself. Camunda is not for that purpose.

You need to distinguish between page/screen-flow and business process / workflow. While I have seen people attempt to use a workflow engine to manage the screen-flow, it is not the most suitable tool for it.Better use the means provided by the UI framework of your choice.
The granularity in a managed workflow is different. Different tasks have different UIs associated with them and this creates a flow when it is the same user but the idea is a coarser granularity than screen-flow. A task (as in unit of work) could potentially have multiple screens. Between different task you usually have the potential for a change of the performer of the tasks (role based work assignment).