This commit adds the functionality necessary to transition from
doing binary verification on the basis of a single signature to
requiring a minimum threshold of trusted signatures.
A signature can appear as "good" from GPG output, but it may not come
from an identity the user trusts. We call these "good, untrusted"
signatures.
We report bad signatures but do not necessarily fail in their presence,
since a bad signature might coexist with enough good, trusted signatures
to fulfill our criteria.
If "--import-keys" is enabled, we will prompt the user to
optionally try to retrieve unknown keys. Marking them as trusted locally
is a WIP, but keys which are retrieved successfully and appear on the
builder-keys list will immediately count as being useful towards
fulfilling the threshold.
Logging is improved and an option to output JSON that summarizes the
whole sum signature and binary verification processes has been added.
Co-authored-by: Russ Yanofsky <russ@yanofsky.org>
Co-authored-by: willcl-ark <will8clark@gmail.com>
