How to Enable CORS on Node js Production App on Ubuntu 14.04 with Nginx Proxy

I have set up a digital ocean droplet that is a reverse proxy server using nginx and node. I used this tutorial from digital ocean as a starting point

https://www.digitalocean.com/community/tutorials/how-to-set-up-a-node-js-application-for-production-on-ubuntu-14-04.

I have also set up ssl with lets encrypt. The issue I am currently having is that I am unable to make cross domain ajax calls to the server. I am getting a error of No ‘Access-Control-Allow-Origin’ header is present. I have set up the appropriate header response in my node app and have attempted to follow the few examples I could find for nginx with no luck. Below is my code.

nginx

server {
listen 443 ssl;

server_name lefthookservices.com www.lefthookservices.com;

ssl_certificate /etc/letsencrypt/live/lefthookservices.com/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/lefthookservices.com/privkey.pem;

 ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
    ssl_prefer_server_ciphers on;
    ssl_dhparam /etc/ssl/certs/dhparam.pem;
    ssl_ciphers 'ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-$
    ssl_session_timeout 1d;
    ssl_session_cache shared:SSL:50m;
    ssl_stapling on;
    ssl_stapling_verify on;
    add_header Strict-Transport-Security max-age=15768000;

location / {


     proxy_set_header 'Access-Control-Allow-Origin' 'https://exponential.singularityu.org';
        proxy_set_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS, PUT, DELETE';
        proxy_set_header 'Access-Control-Allow-Headers' 'X-Requested-With,Accept,Content-Type, Origin';

        proxy_pass http://127.0.0.1:8080;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-for $proxy_add_x_forwarded_for;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;




}
  location ~ /.well-known {
           allow all;
    }

}

server {
    listen 80;
    server_name lefthookservices.com  www.lefthookservices.com;
    return 301 https://$host$request_uri;
}

Here is my app.js script using express

'use strict';
var colors = require('colors/safe');

var express = require('express');

var knack = require('./knack_call.js');

var bodyParser = require('body-parser');

var cors = require('cors');

colors.setTheme({
 custom: ['blue', 'bgWhite']
});

var app = express();

app.use(bodyParser.json());


// allow for cross domain ajax

app.get('/',  function(request, response){

   response.send('hello\n');

});

app.post('/', function(request, response){

   response.header("Access-Control-Allow-Origin", "*");
   response.header("Access-Control-Allow-Headers", "X-Requested-With");
   response.header("Access-Control-Allow-Methods', 'GET,POST");

   knack.getData(request, response);
});

app.listen(8080, '127.0.0.1', function(m){
   console.log(colors.custom("Captin the server is at full strength"));
});

Any suggestion that could help me set the correct headers to allow CORS would be greatly appreciated. Thank you in advance