Not able to execute flows in vco orchestrator server thru a proxy server

Server A needs to execute flows on VCO Server C. Server A need to connect thru a Proxy server B to reach VCO server C.

We are able to login to VCO Server, create session and workflow object, but when trying to perform workflow.execute, we see the exception as "Connection refused". Has anyone gone thru executing VCO workflows thru a proxy server? How to resolve "Connection refused" eror.

Exception:

org.springframework.web.client.ResourceAccessException: I/O error: Connection tohttps://serverc.test.net:8281 refused; nested exception is org.apache.http.conn.HttpHostConnectException: Connection to https://serverc.test.net:8281 refused

               at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:453)

               at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:401)

               at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:199)

               at com.vmware.o11n.sdk.rest.client.services.PresentationService.getPresentation(PresentationService.java:32)

               at com.savvis.symphony.vco.client.WorkflowRunner.execute(WorkflowRunner.java:67)

Code where Error happens:

        if (workflow == null) {

            LOG.error("workflow with id " + params.getWorkflowId() + " does not exist");

            thrownew Exception("workflow with id " + params.getWorkflowId() + " does not exist");

        } else {

            LOG.info("you are going to execute: '" + workflow.getName() + "'");        

            workflowExecution = execute(workflow, session, targetWorkFlow.getExecutionContext());

        }

        return workflowExecution;

    }

    privatestatic WorkflowExecution execute(Workflow workflow, VcoSession session, ExecutionContext builderCtx) throws IOException, InterruptedException {

      WorkflowExecution workflowExecution = null;

        PresentationService presentationService = new PresentationService(session);

        Presentation presentation = presentationService.getPresentation(workflow);

        PresentationExecution presentationExecution = presentationService.createPresentationExecution(presentation,

               builderCtx);