code: func (h *Handler) ExportPrivateKey(tkn, account string) ([]byte, error) {
  	logger := h.logger.Add("method", "ExportPrivateKey",
  		"account", account)
  	if !h.token.Check(tkn) {
  		logger.Warn("access denied")
  		return nil, ErrAccessDenied
  	}
  
  	var acc data.Account
  	err := h.db.FindByPrimaryKeyTo(&acc, account)
  	if err != nil {
  		logger.Error(err.Error())
  		if err == reform.ErrNoRows {
  			return nil, ErrAccountNotFound
  		}
  		return nil, ErrInternal
  	}
  	key, err := data.ToBytes(acc.PrivateKey)
  	if err != nil {
  		logger.Error(err.Error())
  		return nil, ErrInternal
  	}
  
  	return key, nil
  }
docs: // ExportPrivateKey returns a private key in base64 encoding by account id.