Facebook page and canvas apps with Rails 4, can lead to a blank white page. In Rails 4, the X-Frame-Options are sets by default, and you should override them, to allow iframes in Rails.

facebook_apps_controller.rb

class FacebookClubsController < ApplicationController
  layout "facebook_canvas"

  after_filter :allow_iframe

  def index
  end

  private
  
  def allow_iframe
    response.headers["X-Frame-Options"] = "GOFORIT"
  end
end

Note:

It is probably a bit safer to whitelist to the facebook domain using:

response.headers['X-Frame-Options'] = "ALLOW-FROM https://www.facebook.com"