code: func (c *Client) SignedWrite(handle uint16, value []byte, signature [12]byte) error {
  	if len(value) > c.l2c.TxMTU()-15 {
  		return ErrInvalidArgument
  	}
  
  	// Acquire and reuse the txBuf, and release it after usage.
  	txBuf := <-c.chTxBuf
  	defer func() { c.chTxBuf <- txBuf }()
  
  	req := SignedWriteCommand(txBuf[:15+len(value)])
  	req.SetAttributeOpcode()
  	req.SetAttributeHandle(handle)
  	req.SetAttributeValue(value)
  	req.SetAuthenticationSignature(signature)
  
  	return c.sendCmd(req)
  }
docs: // SignedWrite requests the server to write the value of an attribute with an authentication
  // signature, typically into a control-point attribute. [Vol 3, Part F, 3.4.5.4]