tl;dr: if you upload files to GCS from inside the SDK, please describe your use cases and why running outside the SDK wouldn't work
we currently pass into the SDK any ~/.boto creds we find outside of the SDK. if the user doesn't have any, we fallback to the chromeos-overlay copy (if it exists in your source checkout). i'm planning on changing the logic to never pass in user creds from outside the SDK, and only ever use the chromeos-overlay one.
these creds are used by some commands people run inside the SDK (including manual `gsutil`). notably, they are *not* used when building packages -- our build logic will use the per-overlay boto files instead.
by passing along the chromeos-overlay copy, you'd still get read-only access to internal artifacts that bots/builds would use. i'm not sure even this is necessary, but i'm stripping away layers one at a time :).