Which Google API's require that you impersonate a user and which require that you do not? <p>Using a service key: In the Gmail API, for example, I must impersonate the user to access their email. To access their calendar, however, I get an “error: unauthorized client” unless I remove the line impersonating the user. I then have to instead go to Calendar and share that calendar with the service account. Why? Surely, if I'm impersonating a user then they have access to their own calendars.</p>