Wow, this was an amazingly smooth process, congratulations to everybody involved.
I wondered: in other sites where I log in with Google, I get presented with a permissions screen (see below what happens at Edmodo), but not here. I guess Moodle doesn't need any permissions at this point?
I think I understand it: the permission to access Drive, for example, is asked for when I start using the Drive repository in the file picker. That seems like an excellent UX choice.