title: Omniauth + facebook not working as expected
body: <p>I am new to Omniauth. I am making a toy application. It displays a random sentence and that's all. I am using Sinatra + Omniauth. I would like to make it a Facebook application.
   I basically followed this tutorial:
  <a href="http://devcenter.heroku.com/articles/facebook" rel="nofollow">http://devcenter.heroku.com/articles/facebook</a>
  (current app at: <a href="http://frasesbarrio.heroku.com/" rel="nofollow">http://frasesbarrio.heroku.com/</a> )</p>
  
  <p>I have pointed the fb app to <a href="http://frasesbarrio.heroku.com/" rel="nofollow">http://frasesbarrio.heroku.com/</a></p>
  
  <p>I have this code:</p>
  
  <pre><code>use OmniAuth::Builder do
    provider :facebook, APP_ID, APP_SECRET, { :scope =&gt; 'status_update, publish_stream, offline_access' }
  end
  
  
  get '/auth/facebook/callback' do
  #  raise "auth facebook"
    session['fb_auth'] = request.env['omniauth.auth']
    session['fb_token'] = session['fb_auth']['credentials']['token']
    session['fb_error'] = nil
  
    redirect '/'
  end
  </code></pre>
  
  <p>And I have several problems:</p>
  
  <p>When an user request the FB app, Facebook issues a POST on my /
  I think this is weird because I have not seen anything similar in any tutorial. 
  I have just :</p>
  
  <pre><code>post '/' do  
  
    redirect "http://localhost:4567/auth/facebook"
  
    get_sentence  
    @ranking = get_ranking
    erb :index
  end
  </code></pre>
  
  <p>Doing so, the user will be redirected to application on canvas facebook page with a big facebook sign, if the user clicks on it the authentification continues and he is redirected to /.</p>
  
  <p>I mean redirected completely, outside the facebook canvas and domain. </p>
  
  <p>I have seen several tutorials and everyone is doing the same than me, so I really don't know what can be happening. </p>