Revert recent changes in get_auth_token()

[francisbarton]

Something about the change to this function means it is no longer finding or refreshing existing tokens as expected, and is instead regularly (always?) asking for a manual (web-based) refresh. This seems to mean that when it is called within a wrapper function, if get_auth_token() is waiting for manual refresh - which doesn't get surfaced - the wrapper function hangs indefinitely while waiting.

edit: reverting to use v1 auth tokens seems to fix the problem - but further testing in the wild may be required.

[francisbarton]

Closed by #81