code: func (m *MemoryStorer) All() ([]string, error) {
  	m.mut.RLock()
  	defer m.mut.RUnlock()
  
  	sessions := make([]string, len(m.sessions))
  
  	i := 0
  	for id := range m.sessions {
  		sessions[i] = id
  		i++
  	}
  
  	return sessions, nil
  }
docs: // All keys in the memory store