I think some annotations in the camunda-engine-rest-core services interface might be incomplete in the @Consumes annotation.
I found an issue when trying to use the UserRestService.createUser method thru a generic rest client like jboss resteasy. I get a HTTP 415 error for incorrect media type.
I think the annotation should be
like other post services (eg GroupRestService.createGroup).
I solved the situation creating a derived interface with the correct annotation, but it should not be necessary.