Fetching signed_request in a Facebook App with Ruby/Sinatra and the Rest-Graph gem

I've built a Facebook app using Sinatra and the Rest-Graph gem. Now I would like to embed the app as an iframe tab in a Facebook Page.

To do that, I need to fetch d开发者_JAVA技巧ata from the signed_request sent to my app by Facebook.

The Rest-Graph gem states the following feature on its Github page:

Utility to extract access_token and check sig in cookies/signed_request

I couldn't find any documentation on how to use this "utility". Can you point me to some documentation or even better, give me an example on how this is used with Ruby/Sinatra?

---

Nearly all of the Graph API libraries that are available deal with signed_request in a similar way. Rest-Graph has a parse_signed_request method (Rest-Graph/lib/core.rb) that you can call in Sinatra.

I'm using Koala for this with Sinatra, and it works as advertised:

oauth = Koala::Facebook::OAuth.new(APP_ID, APP_CODE)
signed_request = oauth.parse_signed_request(params["signed_request"])

You get back a hash of the JSON object that Facebook posts:

{
"algorithm"=>"HMAC-SHA256",
"issued_at"=>1303883452, 
"user"=> 
{
"country"=>"us",
"locale"=>"en_US"
},
"user_id"=>"100002364226618"
}

rest-graph makes it pretty easy, too. Just tested this in a Sinatra app. Works perfectly:

rg = RestGraph.new( :app_id => APP_ID, :secret => APP_SECRET)
parsed_request = rg.parse_signed_request!(params["signed_request"])

Lemme know if that doesn't work for you.

---

I just got a response to this question from "cardinalblue", the developer of the Rest-Graph gem. This little example was exactly what I was looking for:

require 'sinatra'
require 'rest-graph'

app_id = '123'
secret = 'abc'
config = {:app_id => app_id,
          :secret => secret}

post '/' do
  rg = RestGraph.new(config)
  rg.parse_signed_request!(params['signed_request'])
  "#{rg.get('me').inspect.gsub('<', '&lt;')}\n"
end

run Sinatra::Application

Sidenote: In case you're building something similar, please note the post '/' do. Facebook Pages fetch your page using a POST request instead of a GET.