Adding a subscribed/shared Google Calendar calendar to iPhone (iOS 12)

This is actually an answer, not a question. Based on the number of people who've had this problem, it's something Apple screwed up years ago, and still hasn't fixed.

You would *think* you could add your Google Calendars to your iOS calendar by going to "Settings" -> "Passwords & Accounts" and adding a Google account. This *might* work if you have a GMail account. I, and many other people, DO NOT USE GMAIL. I know there are people out there who are totally unaware that you can have a Google account without having ever had an email address that ends in "gmail.com". Trust me, it's a thing.

There are quite a few sites that explain that you can get around this failure in iOS by setting up an Exchange account, but filling in the "server" part of the form with "m.google.com". That doesn't work any more either.

I tried setting up an "Other -> CalDAV" account. Still no luck.

Eventually I hacked the configuration files on my Mac to find out what I needed to know to get the calendar to show up on my iPhone. So! Here we go:

1. Go to calendar.google.com -> Settings (the gear in the upper right) -> Settings (from the pop-down menu)

2. Click on the calendar you want to add (should be listed under "Settings for other calendars")

3. Click on or scroll down to the "Integrate Calendar" section. Find the "Calendar ID." You'll need this in a minute.

(the following steps might not be necessary if you don't have 2-factor authentication turned on. If you don't, why on earth not?)

4. Now go to "accounts.google.com" -> Sign-in and Security -> Signing in to Google -> App Passwords

5. You need to generate an app-specific password. Scroll to the bottom of the page to find the part where you can generate a new password. It will come up as four four-letter 'words.' I think you can enter it either with or without the spaces, but I entered mine without. For now, just make a note of this password as well. (You can just leave the browser window open.)

6. On your iPhone, go to Settings -> Passwords & Accounts -> Add Account -> Other -> Add Subscribed Calendar

7. In the Server field enter

https://calendar.google.com/calendar/dav/[the_calendar_ID]/events/

My calendar ID was an email address, so it had an @ in the middle. The URL I extracted from one of Calendar's "*.info" files had replaced that with "%40". I don't know if escaping the @ by replacing it with the code is required or not. In case it's not clear, just put the calendar ID from the Google Calendar page between the / and the other /. Don't include the [ and ] around your calendar ID.

8. You should then be asked for a username and password. The username is your Google account username, which is some kind of email address. For the password, use the app-specific password from Step 5.

9. Click "Done." With any luck, your phone will verify the account and pop you back to the Passwords account screen with your subscribed calendar now on the list.

If this doesn't work, you might have to tell Google to enable sync-ing of that calendar. I'd already done this while trying to get other people's instructions to work, so I'm not sure if it's needed or not. Google does not enable sync on shared calendars by default, and as far as I can tell, there is absolutely no way to get to the sync settings page from the Google Calendar itself. You have to know about the Secret URL: https://calendar.google.com/calendar/syncselect

On this page, you can check the box for your shared calendar.