code: func (e *Engine) CloneMembership(ctx context.Context, encMec, mecNonce []byte, privKP *EncryptionKeyPair, encPubKey, targetPubKey []byte) ([]byte, []byte, error) {
  	mek, err := e.Unbox(ctx, encMec, mecNonce, privKP, encPubKey)
  	if err != nil {
  		return nil, nil, err
  	}
  	defer mek.Destroy()
  
  	return e.Box(ctx, mek, privKP, targetPubKey)
  }
docs: // CloneMembership decrypts the given KeyringMember object, and creates another
  // for the targeted user.