form_authenticity_token (ActionController::RequestForgeryProtection)

    # File lib/action_controller/request_forgery_protection.rb, line 107
          def form_authenticity_token
            @form_authenticity_token ||= if !session.respond_to?(:session_id)
              raise InvalidAuthenticityToken, "Request Forgery Protection requires a valid session.  Use #allow_forgery_protection to disable it, or use a valid session."
            elsif request_forgery_protection_options[:secret]
              authenticity_token_from_session_id
            elsif session.respond_to?(:dbman) && session.dbman.respond_to?(:generate_digest)
              authenticity_token_from_cookie_session
            else
              raise InvalidAuthenticityToken, "No :secret given to the #protect_from_forgery call.  Set that or use a session store capable of generating its own keys (Cookie Session Store)."
            end
          end