Dynamics CRM 2011 - Trigger a workflow from JavaScript

Recently I had a requirement to trigger a workflow on click of ribbon button when it meets certain criteria. Refer below link for calling JavaScript function from custom ribbon button.
http://ankit.inkeysolutions.com/2012/01/crm-2011-how-to-use-visual-ribbon.html
The criteria values are checked using JavaScript and if all criteria are satisfied then the workflow is to be triggered. The function below will take two inputs where entityId is the id of the record for which the workflow will execute and workflowProcessId is the id of the workflow which we want to execute. 

function startWorkflow(entityId, workflowProcessId) {

  var xml = "" +    "<?xml version=\"1.0\" encoding=\"utf-8\"?>" +

 "<soap:Envelope xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\">" +  Xrm.Page.context.getAuthenticationHeader() +  "<soap:Body>" +"<Execute xmlns=\"http://schemas.microsoft.com/crm/2007/WebServices\">" +"<Request xsi:type=\"ExecuteWorkflowRequest\">" +"<EntityId>" + entityId + "</EntityId>" +  "<WorkflowId>" + workflowProcessId + "</WorkflowId>" + "</Request>" +"</Execute>" +"</soap:Body>" +"</soap:Envelope>";

var xmlHttpRequest = new ActiveXObject("Msxml2.XMLHTTP");

xmlHttpRequest.Open("POST", "/mscrmservices/2007/CrmService.asmx", false);

xmlHttpRequest.setRequestHeader("SOAPAction", "http://schemas.microsoft.com/crm/2007/WebServices/Execute");

xmlHttpRequest.setRequestHeader("Content-Type", "text/xml; charset=utf-8");

  xmlHttpRequest.setRequestHeader("Content-Length", xml.length);

  xmlHttpRequest.send(xml);

}