code: func (s Session) ID() string {
  	if sessionIDStr, ok := s[SessionIDKey]; ok {
  		return sessionIDStr.(string)
  	}
  
  	buffer := uuid.NewV4()
  
  	s[SessionIDKey] = hex.EncodeToString(buffer.Bytes())
  	return s[SessionIDKey].(string)
  }
docs: // ID retrieves from the cookie or creates a time-based UUID identifying this
  // session.