CORS

Use rack-cors to enable CORS.

require 'rack/cors'
use Rack::Cors do
  allow do
    origins '*'
    resource '*', headers: :any, methods: [ :get, :post, :put, :delete, :options ]
  end
end

Alternatively you can set CORS headers in a before block.

before do
  header['Access-Control-Allow-Origin'] = '*'
  header['Access-Control-Request-Method'] = '*'
end