Hack the use of the topcoder API to get the latest challenge data, and create RSS string in the desired format to be consumable in any RSS reader.

topcoder-challenges-webtask.js

'use latest';

var request = require('request@2.56.0');
var xmlbuilder = require('xmlbuilder@2.6.4');

module.exports = function(context, req, res) {
  request({
    method: 'GET',
    uri: 'https://api.topcoder.com/v2/challenges/active?review=COMMUNITY,INTERNAL&type=develop'
  }, function(error, response, body) {
    var rss = xmlbuilder.create({
      'rss': {
        '@version': 2.0
      }
    });

    var channel = rss.ele({
      channel: {
        'title': 'title',
        'link': 'http://link.com',
        'description': 'desc',
        'category': 'cat'
      }
    });
    var challenges = JSON.parse(body).data;
    challenges.sort(function(a, b) {
      return new Date(b.registrationStartDate) - new Date(a.registrationStartDate);
    });
    challenges.forEach(function(challenge) {
      var item = channel.ele('item');
      item.ele('title', challenge.challengeName + ' - $' + challenge.totalPrize);
      var description = 'Type: ' + challenge.challengeType + '|\n' +
                        'Registrants: ' + challenge.numRegistrants + '|\n' +
                        'Current Phrase: ' + challenge.currentPhaseName + '|\n' +
                        'Submission End: ' + challenge.submissionEndDate + '|\n';
      item.ele('description', description);
      item.ele('link', 'https://www.topcoder.com/challenge-details/' + challenge.challengeId);
      item.ele('pubDate', challenge.registrationStartDate);
      challenge.technologies.forEach(function(tech) {
        item.ele('category', tech);
      });
    });
    var xml = channel.doc().end({pretty: true});
		
    res.writeHead(200, { 'Content-Type': 'application/xml '});
    res.end(xml);
  });
}