Log Message:
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tools/syz-aflow: support downloading bugs behind an AppEngine login
Some syzbot dashboard pages are guarded by an AppEngine login page. The
-download flag helps generate an input.json out of a bug report but it
currently uses simple HTTP GET commands without any authentication. When
called on a bug behind a login page, it received a login page HTML
instead of a json payload and fails in confusing ways.
The authentication page can be skipped using an authentication token.
It's easy to retrieve a token from the gcloud auth print-access-token
command.