Add source.NewFromRegistry function so that the syft attest command can always explicitly ask for an OCIRegistry provider rather than rely on local daemon detection for image sources.
Attestation can not be used where local images loaded in a daemon are the source. Digest values for the layer identification step in attestation can sometimes vary across workstations.
This fix makes it so that attest is generating an SBOM for, and attesting to, a source that exists in an OCI registry. It should never load a source from a local user docker/podman daemon.
Signed-off-by: Christopher Phillips <christopher.phillips@anchore.com>
Co-authored-by: Alex Goodman <alex.goodman@anchore.com>
