code: func (m *MemoryStorer) Set(key, value string) error {
  	m.mut.Lock()
  	m.sessions[key] = memorySession{
  		expires: time.Now().UTC().Add(m.maxAge),
  		value:   value,
  	}
  	m.mut.Unlock()
  
  	return nil
  }
docs: // Set saves the value string to the session pointed to by the session id key.