Add debug logging to auth.py.
Add debug logging to auth.py.

There are some mysterious issues happening to some Windows users. Verbose log
can be helpful.

R=maruel@chromium.org
BUG=356813

Review URL: https://codereview.chromium.org/1051143004

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@294910 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools