405 not allowed nginx, CORS? Nginx config? Or something else?

Working on an app built using Ember.js and Rails.
Authentication is being done with ember-simple-auth using Oauth2.
I am able to login to my app locally in my development environment, but as soon as I try to login on my production server (through Heroku) I start receiving a nginx 405 not allowed status code.

First thing I thought was maybe it is my request headers / CORS. I am using rack-cors gem on my rails side and configured it based directly off the readme example. Here is my application.rb

Researching, I found the same problem with the solution being to configure Nginx side of things, but I figured since that is being handled by heroku I wasn't really sure if that was where I need to make my changes.

Let me know if there are any other files/info that could help.

What is the best way to debug this problem?