Integrate public calendars from Google Calendar with PHP + Laravel

I've been researching a lot to find the solution to this problem:

I need to integrate Google Calendar calendars into my system (Laravel) but only find ways to do with authentication (the person allows the API and then manages their own data.) What I want: Register multiple public calendars in the system ( the URL of them) and everyone can view without logging in with the google account, the calendar generated by another Google account. You can do this with iframe with public calendars, however calendars even appear in the search of google, and I need to protect so that only within the system they are possible to visualize.