The account ID whose token should be returned. If not specified, the
function will use an account from the Chrome profile: the Sync account if
there is one, or otherwise the first Google web account.
The enableGranularPermissions flag allows extensions to
opt-in early to the granular permissions consent screen, in which
requested permissions are granted or denied individually.
Fetching a token may require the user to sign-in to Chrome, or
approve the application's requested scopes. If the interactive
flag is true, getAuthToken will
prompt the user as necessary. When the flag is
false or omitted, getAuthToken will
return failure any time a prompt would be required.