@tbanzato I can partly help with this. The secret code is available in your calendar settings - available either through the upper right gear icon -> Settings ->click on the calendar you wish to use in the left hand menu -> scroll all the way down … Or click on the three dot icon that comes up when you hover over the calendar name -> Settings -> scroll all the way down.
Then just copy and paste the “Secret Address in iCal format” into your config file.
(Note to the future - this is as of 11April18 - gods only know what the Google UI may look like tomorrow !)
And before you get excited, I did exactly that…and it doesn’t work, or at least not yet (still figuring that part out.)