How to send CORS headers with Devise if user not authorized (401 response)

Question

I am working on an app, where server and the api-consuming client reside under different domains, so I would like to use CORS. To do so, I have to set corresponding http headers in the server response:

def cors_set_access_control_headers
  headers['Access-Control-Allow-Origin'] = 'http://localhost'
  headers['Access-Control-Allow-Methods'] = 'POST, GET, OPTIONS'
  headers['Access-Control-Allow-Headers'] = '*, X-Requested-With, X-Prototype-Version, X-CSRF-Token, Content-Type'
  headers['Access-Control-Max-Age'] = "1728000"
end

This method is used as a before_filter in ApplicationController.

For some resources the user has to be authenticated and authorized. Requests are done via XHR/Ajax. So if the user is not authenticated Devise will send a 401 response to the client, instead of redirecting to a sign in page. But the filter to set the CORS headers is not used for that response. Thus the 401 response is not sent to the client. I want to catch and use the 401 response in the client.

Currently I am using a workaround by not using the Devise authentication methods, but a custom auth snippet:

def authenticate_cors_user
  if request.xhr? && !user_signed_in?
    error = { :error => "You must be logged in." }
    render params[:format].to_sym => error, :status => 401
  end
end

This is set as a before_filter in ApplicationController, too. This way the filter to set CORS headers gets triggered and everything works fine.

I would prefer to use the default behaviour of Devise, but the CORS headers would have to be set in the 401 response. How to do this? Do I have to configure warden for that?

How could the CORS headers be set for the 401 response generated by Devise instead of creating my own response?

Answer 1

I successfully used the rack-cors gem https://github.com/cyu/rack-cors and outlined my experience on my blog.

Punchline: Specify middleware order so cors handler is before warden:

config.middleware.insert_before Warden::Manager, Rack::Cors