Parsing Facebook's signed_request (in ruby)

gistfile1.rb

  def parse_data
    # This is a typical set of parameters passed by Facebook
    # Parameters: {"signed_request"=>"vsSe9NNeyqom0hAtGyb2L9scc3-aNbY5Xb25EW55LpE.eyJhbGdvcml0aG0iOiJITUFDLVNIQTI1NiIsImV4cGlyZXMiOjEzMDA3NzAwMDAsImlzc3VlZF9hdCI6MTMwMDc2NDg2Niwib2F1dGhfdG9rZW4iOiIxNzE2MDQwOTI4NjgwNTd8Mi4xQnBWNm5mU2VXRm5RT0lOdzltNWFRX18uMzYwMC4xMzAwNzcwMDAwLTE1MjAwMzkxfEFpNXctc2t4WlJyVUd1ZzZvOU95aDZBQmdSZyIsInVzZXIiOnsiY291bnRyeSI6InVzIiwibG9jYWxlIjoiZW5fVVMiLCJhZ2UiOnsibWluIjoyMX19LCJ1c2VyX2lkIjoiMTUyMDAzOTEifQ"}
  
    # If we have the signed_request parameters, stash them away
    session[:signed_request] = params[:signed_request] if params[:signed_request]
  
    encoded_user_data = session[:signed_request]
    return if encoded_user_data.blank?
  
    # We only care about the data after the '.'
    payload = encoded_user_data.split(".")[1]
  
    # Facebook gives us a base64URL encoded string. Ruby only supports base64 out of the box, so we have to add padding to make it work
    payload += '=' * (4 - payload.length.modulo(4))
  
    decoded_json = Base64.decode64(payload)
    @signed_data = JSON.parse(decoded_json)
  
    # This is what your parsed JSON should look like
    # @signed_data => {"expires"=>1300770000, "algorithm"=>"HMAC-SHA256", "user_id"=>"15200391", "oauth_token"=>"171604092868057|2.1BpV6nfSeWFnQOINw9m5aQ__.3600.1300770000-15200391|Ai5w-skxZRrUGug6o9Oyh6ABgRg", "user"=>{"country"=>"us", "locale"=>"en_US", "age"=>{"min"=>21}}, "issued_at"=>1300764866}
  
    #The existance of an oauth token means the user has given permission to the app.
    @oauth_token = @signed_data["oauth_token"]
  end