Use modern gargle secret management

[hadley]

@jennybc I don't think this code is in quite the right place, because ideally I want it to auth automatically for R CMD check and pkgdown. Can you suggest where I should move this code?

[jennybc]

The approach I've settled on in googlesheets4 and googledrive is to have an internal function (e.g. drive_auth_internal()) that auths with a specific service account. (For both of those packages there are two relevant service accounts: one that I use for testing, one that I use for docs (including pkgdown). You don't seem to have that wrinkle here.)

https://github.com/tidyverse/googledrive/blob/74a69a3a1fd66e930802ce6e461538c9e15f7c86/R/drive_auth.R#L285-L347

I then call that function in various places. Most importantly, in tests/testthat/helper.R:

https://github.com/tidyverse/googledrive/blob/74a69a3a1fd66e930802ce6e461538c9e15f7c86/tests/testthat/helper.R#L1-L10

I also call it in, e.g., vignette setup chunks:

https://github.com/tidyverse/googledrive/blob/74a69a3a1fd66e930802ce6e461538c9e15f7c86/vignettes/articles/permissions.Rmd#L6-L9

And, importantly, call it in .onLoad(), if we seem to be building the pkgdown website:

https://github.com/tidyverse/googledrive/blob/74a69a3a1fd66e930802ce6e461538c9e15f7c86/R/zzz.R#L11-L16

[hadley]

Based on run time (60s vs ~16s on main), I'm pretty confident that this is now enabled for pkgdown too.