Not easy but there are varieties some thrives quite well in the shade, It's needs more frequent fertilizing and not to been mowed to short.
If it's to short moss will easily emerge so you have to sprinkle chalk at least twice a year.
Plenty of grass seed suitable for shadier areas Luca. If you take a look in your local GC or Diy store you'll get a good choice.
My front garden is north west facing, so it's in shade a lot of the time. I use a weed and feed product in spring and cut regularly - that keeps it healthy. If necessary, it gets another weed/feed in late summer. It's never cut too short. Never take more than about a third of the length off as cutting to o short weakens the grass and allows weeds to dominate.