Google URL to subscribe to a calendar

Similar to the URL to add an event to someone's Google calendar, does anybody know if there's a URL that can let someone subscribe to an iCalendar URL containing multiple events?

Basically, I run a system with many events, and I'd like to give my users a simple one-click URL to bring ALL of those events into their calendar and subscribe to updates.

Currently, this is possible to do manually:

Open Google calendar
Select Other Calendars > Add > From URL
Enter URL and click Add Calendar

Solution

I think I figured it out but would love more information if anybody is more familiar with this.

NOTE: This doesn't seem to work with https URLs (but maybe that was just a problem with my local SSL cert)

Solution:

Add cid=<URL> to the end of the main Google Calendar URL.

For example:

https://calendar.google.com/calendar/r?cid=http://389d-50-215-20-6.ngrok.io/calendar.ics