code: func (w *HTTPProvider) Present(domain, token, keyAuth string) error {
  	var errs []error
  
  	challengePath := path.Join("/", http01.ChallengePath(token))
  	for _, host := range w.hosts {
  		mc, err := memcache.New(host)
  		if err != nil {
  			errs = append(errs, err)
  			continue
  		}
  		_ = mc.Add(&memcache.Item{
  			Key:        challengePath,
  			Value:      []byte(keyAuth),
  			Expiration: 60,
  		})
  	}
  
  	if len(errs) == len(w.hosts) {
  		return fmt.Errorf("unable to store key in any of the memcache hosts -> %v", errs)
  	}
  
  	return nil
  }
docs: // Present makes the token available at `HTTP01ChallengePath(token)` by creating a file in the given webroot path