Centralized use of requests

Hi,
it would be very helpful if all API calls which are made via requests would be routed through a central extendable method. With this it would be possible to inject individual authentication or other recurring options into the call. Since these calls are currently being made in many different methods of the EngineClient and the ExternalTaskClient, this is difficult to achieve.

If you think this suggestion is a good idea, I would participate in the implementation or make a pull request. I just want to make sure the idea has a change to become accepted.

Best regards and thanks for your work!
Jens