In my domain with Render I use this URL rewrite

www.example.com/library to library.example.com

This works as expected, so if the user visits example.com/library the content is server from a subdomain. The CSS is loaded as expected but I got a CORS error only for JS.

From the dev console, when visiting example.com/library I see

CORS ERROR

GET https://library.example.com/assets/application-ec9fb8976583666f9882e99ffe94f0391fc9ac4f1a32034d128201c87ac33ca3.js

Request headers

• sec-fetch-dest: script
• sec-fetch-mode: cors
• sec-fetch-site: same-site
• Origin: https://www.example.com

/config/application.rb

config.middleware.insert_before 0, Rack::Cors do

      allow do
        origins 'https://www.example.com'
        resource '*', headers: :any, methods: [:get, :post, :put, :patch, :delete, :options, :head]
      end

end

but isn’t working.

I expect no errors in dev console and I must be able to visit example.com/library and load the page served from library.example.com with all CSS and JS.