# File lib/omniauth/strategies/oauth2/facebook.rb, line 52
      def build_access_token
        if !signed_request.nil? && !signed_request.empty?
          verifier = signed_request['code']
          client.auth_code.get_token(verifier, {:redirect_uri => ''}.merge(options))
        elsif !facebook_session.nil? && !facebook_session.empty?
          @access_token = ::OAuth2::AccessToken.new(client, facebook_session['access_token'], {:mode => :query, :param_name => 'access_token'})
        else
          super
        end
      end