# File lib/openid/store/memcache.rb, line 61
      def use_nonce(server_url, timestamp, salt)
        return false if (timestamp - Time.now.to_i).abs > Nonce.skew
        ts = timestamp.to_s # base 10 seconds since epoch
        nonce_key = key_prefix + 'N' + server_url + '|' + ts + '|' + salt
        result = @cache_client.add(nonce_key, '', expiry(Nonce.skew + 5))
        return !!(result =~ /^STORED/)
      end