Description

• Introduce services for user task and job resources, similar to the ProcessInstanceServices.
• Handle brokerClient communication in the services by introducing methods for resource manipulation, e.g. public CompletableFuture<UserTaskRecord> completeUserTask(final long userTaskKey, final DirectBuffer variables, final String action).
• Service methods create and send broker command requests, asynchronously handle the response, map broker errors and rejections to a common CamundaServiceException (allowing access to the rejection and error), and return completable futures.
• The REST controllers validate incoming request data, extract the data for the service methods, call the service methods, and handle the response and potential exception asynchronously like they already do, mapping them to respective REST responses.

Reasoning

• Unified handling of lower-level communication from REST controllers (e.g. to ES/OS and brokers).
• Simplified REST controllers with service access only, nothing more.
• Clear separation of concerns between REST controllers and services.
• Simplified test setup for REST controllers since only service method calls need to be mocked instead of BrokerClient communication.