# File lib/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