    # File lib/action_controller/vendor/rack-1.0/rack/auth/openid.rb, line 321
          def valid_extension?(ext)
            if not %w[NS_URI Request Response].all?{|c| ext.const_defined?(c) }
              raise ArgumentError, 'Extension is missing constants.'
            elsif not ext::Response.respond_to?(:from_success_response)
              raise ArgumentError, 'Response is missing required method.'
            end
            return true
          rescue
            return false
          end