using async module in nodejs returns nothing in response

Question

I'm trying to post to Instagram API to authenticate user, but I'm getting null value as response. Before using async, I used setTimeout but it returned the error you must provide a client_id. This is my previous post regarding the error.
Here is my code:

app.get('/home',function(req,res){
  req.session.code = req.query.code;
  var data = querystring.stringify({
      client_id: process.env.CLIENT_ID,
      client_secret: process.env.CLIENT_SECRET,
      grant_type: "authorizaton_code",
      redirect_uri: "...",
      code: req.session.code
  })
  var options = {
    headers:{
      'content-type': 'application/x-www-form-urlencoded'
    },
      hostname: 'api.instagram.com',
      path: '/oauth/access_token',
      method:'POST',
      port:443
    }
    req.session.data = '';
    async.waterfall([
      function(callback){
        var request = https.request(options,function(resp){
          resp.on('data',function(chunk){
            req.session.data = chunk.toString();
          })
        })
        request.write(data);
        request.end();
        callback(null,req.session.data);
      }
     ],function(err,results){
      res.json(req.session.data||results[0]);
     })
})