Sench Touch with Rails

CORS with Rails Devise

References:
http://blog.carbonfive.com/2012/02/27/supporting-cross-domain-ajax-in-rails-using-jsonp-and-cors/
https://github.com/cyu/rack-cors
http://nelm.io/blog/2011/11/cors-with-sencha-touch/
http://jessehowarth.com/2011/04/27/ajax-login-with-devise

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GEMFILE
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gem 'rack-cors', :require => 'rack/cors'

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config/application.rb
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# Ensure Rack::Cors to run before Warden::Manager used by Devise
config.middleware.insert_before Warden::Manager, Rack::Cors do
  allow do
    origins '*'
    resource '*',
    :headers => :any,
    :methods => [:get, :post, :options]
  end
end

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config/initializers/devise.rb
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config.http_authenticatable_on_xhr = false
config.navigational_formats = ["*/*", :html, :json]

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Custom Devise Sessions Controller: app/controllers/sessions_controller.rb
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class SessionsController < Devise::SessionsController
  
  def create
    if request.xhr?
      resource = warden.authenticate!(:scope => resource_name, :recall => "sessions#failure")
      return sign_in_and_redirect(resource_name, resource)
    else
      super
    end
  end
  
  def sign_in_and_redirect(resource_or_scope, resource=nil)
    scope = Devise::Mapping.find_scope!(resource_or_scope)
    resource ||= resource_or_scope
    sign_in(scope, resource) unless warden.user(scope) == resource
    return render :json => {:success => true, :redirect => stored_location_for(scope) ||     
    after_sign_in_path_for(resource)}
  end

  def failure
    return render:json => {:success => false, :errors => ["Login failed."]}
  end

end

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Custom Devise Sessions Controller: config/routes.rb
=============================================================================================================
devise_for :users, :controllers => {:sessions => 'sessions'}

I'm not using Sencha, but I debugged into Devise and found out that the SessionsController could be simplified for some cases where you don't need the redirect, because Devise::SessionsController#create will trigger #new on failure as you can see in the source code:

class Devise::SessionsController < ApplicationController
# ...
  def create
    resource = warden.authenticate!(:scope => resource_name, :recall => "#{controller_path}#new")
    set_flash_message(:notice, :signed_in) if is_navigational_format?
    sign_in(resource_name, resource)
    respond_with resource, :location => after_sign_in_path_for(resource)
  end

This is my proposed solution (for some reason the request was not setting xhr = true, so I had to check the request format too):

class SessionsController < Devise::SessionsController
  def new
    return super if !(request.xhr? or request.format == :json)
    render json: { success: false, errors: ["Login failed"] }, status: :unauthorized
  end
end

The logic behind is that you don't need to render sessions#new on an API request, because you're supposed to have a registration endpoint in your API, therefore you can render unauthorized access. Hope it helps.