Example

var map = L.Map('divmap', {
   crs : L.geoportalCRS.EPSG27572
 }).setView();
 var lyr = L.geoportalLayer.WMTS(
   {
     layer : "ORTHOIMAGERY.ORTHOPHOTOS.BDORTHO.L93",
     apiKey : "wqxljfvklsdhvlfkjqfmlq787645"
   },
   {
     attribution : "test for layer ORTHOIMAGERY",
     opacity : 1,
     transparent : true,
     minZoom : 1,
     maxZoom : 21
     ...
   });

 lyr.addTo(map); // ou map.addLayer(lyr);