authenticity_token_from_session_id (ActionController::RequestForgeryProtection)

    # File lib/action_controller/request_forgery_protection.rb, line 120
          def authenticity_token_from_session_id
            key = if request_forgery_protection_options[:secret].respond_to?(:call)
              request_forgery_protection_options[:secret].call(@session)
            else
              request_forgery_protection_options[:secret]
            end
            digest = request_forgery_protection_options[:digest] ||= 'SHA1'
            OpenSSL::HMAC.hexdigest(OpenSSL::Digest::Digest.new(digest), key.to_s, session.session_id.to_s)
          end