SFCC HTTP Service: Making external REST API Call

sfcc-helloworld-service.js

/**
 * Your 1st Hello worldService
 *
 */
var LocalServiceRegistry = require('dw/svc/LocalServiceRegistry');

/**
 * Helloworld
 * @returns {Object} Helloworld Service
 */
function getHelloworldService() {
    var helloworldService = LocalServiceRegistry.createService('test.http.helloworld', {
        createRequest: function (svc, args) {
            // authorization
            var user = svc.getConfiguration().getCredential().getUser();
            var password = svc.getConfiguration().getCredential().getPassword();
            svc.addHeader('Authorization', 'Bearer user="' + user + '",password="' + password + '"');
            svc.addHeader('Content-Type', 'application/json');

            if (svc.getRequestMethod() === 'POST') {
                return JSON.stringify(args);
            }
            return svc;
        },
        parseResponse: function (svc, output) {
            return output;
        },
        getRequestLogMessage: function (reqObj) {
            return reqObj;
        }
    });
    return helloworldService;
}

// export
module.exports = {
    /**
     * Hello World
     * @returns {Object} Helloworld Service
     */
    initHelloworldService: function () {
        var helloworldService = getHelloworldService();
        helloworldService.setRequestMethod('POST');
        helloworldService.setURL(helloworldService.getURL() + '/your-api-endpoint/hello-world');
        return helloworldService;
    }
};

And to pass params to the POST request?