How to enable CORS in Rails 4 App

Rack::Cors provides support for Cross-Origin Resource Sharing

Steps to enable rackcors :

1. Add this gem to your Gemfile:

   gem 'rack-cors'

2. Add the code below to config/application.rb

If you are using Rails 3/4:

config.middleware.insert_before 0, "Rack::Cors" do
  allow do
    origins '*'
    resource '*', :headers => :any, :methods => :any
  end
end

If you are using Rails 5:

config.middleware.insert_before 0, Rack::Cors do
  allow do
    origins '*'
    resource '*', headers: :any, methods: :any
  end
end

You should use rack cors

It provides a nice DSL, to use in your config/application.rb, instead of the messy header work and before filters.

A very permissive would be as follows, but of course, you'll have to tailor it a bit.

use Rack::Cors do
  allow do
    origins '*'
    resource '*', headers: :any, methods: :any
  end  
end