Accessing backend service with Apigee JavaScript policy

[tsuni_ohsaki]

We are trying to make RESTful POST request from JavaScript policy in an Apigee proxy to talk to our service endpoint and having trouble making it work. Our JavaScript code follows the pattern found in api-platform-samples/sample-proxies/outbound-oauth/apiproxy/resources/jsc/api-token-get.js. 

From TRACE tab, I found this line

print('responseObj: ' + JSON.stringify(responseObj));

outputs:

responseObj: undefined

We tested the endpoint itself with Postman and verified it works fine. Is the way httpClient is used in the code correct? 

try
{
    var key = context.getVariable(<variable name in string here>)
    var user = context.getVariable(<variable name in string here>)
    var password = context.getVariable(<vvariable name in string here>)

        url = <RESTful URL here>
        ...
        var bodyObj = {
            'Key': key,
            'User': user,
            'Password': password,
        };
        var req = new Request(url, 'POST', {}, serializeQuery(bodyObj));
        var exchange = httpClient.send(req);

        // Wait for the asynchronous POST request to finish
        exchange.waitForComplete(5000);

        if(exchange)
        {
            if (exchange.isSuccess()) 
            {
                var responseObj = exchange.getResponse().content.asJSON;
                print('responseObj: ' + JSON.stringify(responseObj));     
        ...
}

catch (err) {

    // Code to handle any error that may have happened previously by generating a response
    ...
}

function serializeQuery(obj) {
  var str = [];
  for (var p in obj) {
    str.push(encodeURIComponent(p) + "=" + encodeURIComponent(obj[p]));
  }
  return str.join("&");
}