CODE EXAMPLE FOR JAVASCRIPT

url fetch app pass payload and headers

var options =
{
  "method" : "post",
  "contentType" : "application/json",
  "headers" : {
    "Authorization" : "Basic <Base64 of user:password>"  
  },
  "payload" : '{ "endDate": "2012-06-03" }'
};

UrlFetchApp.fetch(YOURURL,options)