Should an explicit dependency on google-auth be added?

[crwilcox]

It seems we don't currently have an explicit dependency on google-auth, though testing requires it. I reverted a change I made as part of async work, but am making this issue to consider further discussion on this. I am guessing we have a use or resumable media that isn't using google-auth?

13ede91

[crwilcox]

To be clear, I can't find a non-transitive use, but it is basically required as part of credentialing. This may not be an error at all, but wanted to raise it as a point of discussion in case anyone had opinions.