ClientResource client = getAuthenticatedClient("process-instance");
ObjectNode requestNode = objectMapper.createObjectNode();
requestNode.put("processDefinitionKey", "simpleProcess");
requestNode.put("var1", "test");
requestNode.put("var2", 1);
Representation response = client.post(requestNode);
JsonNode responseNode = objectMapper.readTree(response.getStream());
assertNotNull(responseNode);
String processInstanceId = responseNode.get("processInstanceId").asText();