Essentially I've noticed that when a user's primary email is updated on their google account, their calendar ID will also change (e.g. ID will change from john@company.com to john_new@company.com).
This is a problem because I work on an application that relies on the calendar ID being a stable identifier for users. For example, lets say user A at a company schedules an event to their calendar through my application. We'll save metadata related to that event in our own database along with user A's calendar ID to denote that the event was scheduled to that calendar. This is important because we use this information to ensure that only users with write access to this calendar ID can edit this event from our application (important for security purposes).
Lets say user A gets their primary email updated, which causes their calendar ID to also change. Now, when I query the CalendarList endpoint to get a list of user A's calendars, I get back the new calendar ID, which makes my application think that user A should not have access to edit the event they just scheduled since that event was scheduled to a calendar ID that user A no longer has access to.
Is there a way around a problem like this? I can't find an endpoint that will return user A's "archived" calendar ID in addition to their new one. More deeply, I don't understand why their calendar ID changes as it feels like IDs should be stable identifiers...