I don't understand why but in many topics I see that to get and admin route url with secure key and parameter I only need to use :
$this->urlBuilder->getUrl('adminhtml/myroutename/mycontroller/myaction', array('myparam' => 'myvalue'))
and urlBuilder I a Magento\Framework\UrlInterface object.
But in front, I get this URL: http://mysite.lan/adminhtml/myroutename/mycontroller/myparam/myvalue/
And if I remove the adminhtml I get this URL: http://mysite.lan/myroutename/mycontroller/myaction/myparam/myvalue/
So how can I create a correct admin URL with the key and the params?