Ok.  I last posted about how to find the full URL to your icloud calender so you can connect and sync to it using third party apps.  This required diving into a .plist file on a system running macOS.  It is still possible to gather the information needed to to string together the “secret” address.  It seems convoluted at first but also demonstrates a good technique for “spying” on your browsing session and seeing what is going on behind the curtain.

You will need three ingredients for to string together your CalDAV address:

a. your calendar’s server address (especially, the number xx in pxx-caldav.icloud.com)

b. your user ID (dsid)

c. the name of the calander you want to connect to (cal_name)

You can either use Firefox’ or Chrome’s functionality to look at the network; I will continue with Firefox (identical to Chrome, Chromium and iceweazle) for this explanation.

1. Logging in to your iCloud account using the browser.
2. Click/select the address field (where it says icloud.com) Press Ctrl + Shift + I and reload the page.
3. In the debug panel that opens on the bottom of the browser, sort the “Domain” column
4. checking the domain or just hovering over the links, you can find the xx in pxx, this is your specific server; the remainder of the domain does not matter (information a)
5. I then clicked on one entry with domain pxx-calendarws.icloud.com
6. in the new panel that opens to the side, you can click on Headers and find dsid somewhere below under Query string parameters; alternatively, you can find it in the URL; dsid corresponds to your user id (information b)
7. On your iCloud Calender page there on the left will be the names of the calendars you.  easy

There we have it.  The URL to use in  you CalDAV compatible application.

https://pxx-caldav.icloud.com/dsid/calanders/cal_name

see: Your Apple “secret” CalDAV address