code: func (r *keyring) Lock(passphrase []byte) error {
  	r.mu.Lock()
  	defer r.mu.Unlock()
  	if r.locked {
  		return errLocked
  	}
  
  	r.locked = true
  	r.passphrase = passphrase
  	return nil
  }
docs: // Lock locks the agent. Sign and Remove will fail, and List will empty an empty list.