I am upgrading Rails application from Rails 4.1.1 to Rails 5.1.4. 
I have 2 applications, One is Web app(using for angular), and other is API app. 
What I am doing, I am sending request from Web app(Rails with Angular) and fetching data from API app. But when I send request from Web app got error mentioned below:
Failed to load http://api.myapp:3001/user: Response to preflight request doesn't pass access control check: The value of the 'Access-Control-Allow-Origin' header in the response must not be the wildcard '*' when the request's credentials mode is 'include'. Origin 'http://myapp:3000' is therefore not allowed access. The credentials mode of requests initiated by the XMLHttpRequest is controlled by the withCredentials attribute.
http://myapp:3000' -> Web application and request sending to API
http://api.myapp:3001/user -> API application to send response
After google the issue, I found one gem called rack-cors. 
In Web and API both application, I have added 
config.middleware.insert_before 0, Rack::Cors do
  allow do
    origins '*'
    resource '*', :headers => :any, :methods => [:get, :post, :options]
  end
end
But still getting the issue. Please let me know.
 
    