Fix Rails oauth facebook x-frame-options sameorigin error

Question

I can't for the life of me get my Facebook canvas app to display. Chrome console displays this error and nothing shows up inside the iframe - it's blank:

Refused to display 'http://mysite.dev/' in a frame because it set 'X-Frame-Options' to 'SAMEORIGIN'.

I'm using Rails 4.0.0.rc1 and omniauth-facebook 1.4.1, following the Railscast on Facebook Authentication as a guide. I didn't use any of the Javascript code since it was optional and ideally the app should only be accessed within Facebook.

routes.rb

  match 'auth/:provider/callback', to: 'sessions#create', via: [:get, :post]
  match 'auth/failure', to: redirect('/'), via: [:get, :post]
  match 'signout', to: 'sessions#destroy', as: 'signout', via: [:get, :post]

sessions_controller.rb

class SessionsController < ApplicationController

  def create
    user = User.from_omniauth(env["omniauth.auth"])
    session[:user_id] = user.id
    redirect_to root_url
  end

  def destroy
    session[:user_id] = nil
    redirect_to root_url
  end

application_controller.rb

I had to comment this out because I kept getting InvalidAuthenticityToken errors which cost me the other half of my day. A bit more on that here.

  # protect_from_forgery with: :exception

Facebook settings

• App domain: myapp.dev
• Canvas URL: http://myapp.dev
• Secure Canvas URL: -- blank -- if https is specified, I get webpage is unavailable

Please help before I start flipping desks. :)

Answer 1

In Rails 4, X-FRAME-OPTIONS is set to SAMEORIGIN in the headers, which I guess prevents it from being loaded in a frame, as described in this issue. One person notes the difficulty this will cause Facebook app developers.

I managed to solve this by adding the following to application.rb:

config.action_dispatch.default_headers[:'X-Frame-Options'] = "ALLOW-FROM https://apps.facebook.com"

I also used Forward to create a domain to allow Facebook to access my local development machine. I entered this domain in the canvas and secure canvas fields in Facebook. Highly recommended.

Further info here:

• http://blogs.msdn.com/b/ieinternals/archive/2010/03/30/combating-clickjacking-with-x-frame-options.aspx
• https://developer.mozilla.org/en-US/docs/HTTP/X-Frame-Options

Answer 2

I found this part of the edge guide, which explains Rails 4's default headers, to be useful:

http://edgeguides.rubyonrails.org/security.html#default-headers

Here is the main point, copied and pasted:

Every HTTP response from your Rails application receives the following default security headers.

config.action_dispatch.default_headers = { 'X-Frame-Options' => 'SAMEORIGIN', 'X-XSS-Protection' => '1; mode=block',
'X-Content-Type-Options' => 'nosniff' }

You can configure defaultheaders in config/application.rb.

config.action_dispatch.default_headers = { 'Header-Name' => 'Header-Value', 'X-Frame-Options' => 'DENY' }

Or you can remove them.

config.action_dispatch.default_headers.clear