code: func (c *Client) createTx(tokenTx []byte) ([]byte, error) {
  	payload := &common.Payload{Data: tokenTx}
  	payloadBytes, err := proto.Marshal(payload)
  	if err != nil {
  		return nil, err
  	}
  	signature, err := c.SigningIdentity.Sign(payloadBytes)
  	if err != nil {
  		return nil, err
  	}
  	envelope := &common.Envelope{Payload: payloadBytes, Signature: signature}
  	return proto.Marshal(envelope)
  }
docs: // TODO to be updated later to have a proper fabric header
  // createTx is a function that creates a fabric tx form an array of bytes.