Use current auth

[fhinkel]

Use auth how it's meant to be used, see https://github.com/googleapis/google-auth-library-nodejs.

[grant]

@fhinkel Can you add more detail to this bug? Which specific samples does this cover?

This bug was found via bug b/133157557.

[fhinkel]

Closing due to inactivity.