We need this to figure out which authenticator to use, so we need to
override the initial "bootstrap" authenticator.
Bug: b/348024314
Change-Id: I52c5b1db83bc4e2a0a1ec2a07155d352b593cde4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5651288
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
Commit-Queue: Allen Li <ayatane@chromium.org>