Multiple optional arguments with tcolorbox

I would like to produce boxes from tcolorbox which can take two optional arguments, but I’m not sure where to start with. Here is my current MWE :

documentclass{article}
usepackage[utf8]{inputenc}
usepackage[most]{tcolorbox}
usepackage{lipsum}

def ifempty#1{deftemp{#1} ifxtempempty }

newtcolorbox[auto counter,number within=chapter]{definition}[1][]{title={ Définition thetcbcounter ifempty{#1} else --- #1 fi}}

begin{document}

begin{definition}[Matrices]
lipsum[1]
end{definition}

end{document}

This is made such that every single box has a counter depending on the chapter we’re in. An optional argument can be added in case I would want to give a specific name to the box. I would like to add a second optional argument to add a label (to be able to reference to it) to the box. I can add a key label= to the color box but I’m not sure about how to add a second optional argument that would fill that key.

How can I add a second argument to the tcolorbox that would add a label=#2 to the list of arguments of the tcolorbox?

documentclass{book}
usepackage[utf8]{inputenc}
usepackage[most]{tcolorbox}
usepackage{lipsum}

%def ifempty#1{deftemp{#1} ifxtempempty }
%
%newtcolorbox[auto counter,number within=chapter]{definition}[1][]{title={ Définition thetcbcounter ifempty{#1} else --- #1 fi}}

newtcbtheorem[auto counter,number within=chapter]{definition}{Définition}{}{def}

begin{document}
chapter{First}

begin{definition}{Matrices}{a}
lipsum[2]
end{definition}

As can be seen in Definition~ref{def:a} dots

begin{definition}{}{b}
lipsum[2]
end{definition}

As can be seen in Definition~ref{def:b} dots

end{document}