code: func (r *keyring) Unlock(passphrase []byte) error {
  	r.mu.Lock()
  	defer r.mu.Unlock()
  	if !r.locked {
  		return errors.New("agent: not locked")
  	}
  	if len(passphrase) != len(r.passphrase) || 1 != subtle.ConstantTimeCompare(passphrase, r.passphrase) {
  		return fmt.Errorf("agent: incorrect passphrase")
  	}
  
  	r.locked = false
  	r.passphrase = nil
  	return nil
  }
docs: // Unlock undoes the effect of Lock