Use a struct as an input, so that the parameters are named and
we minimize risk of inconsistencies, and make it easier to add more sources.

Should not change behavior.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

Extend loadBytesFromConfigSources to return multiple values, and to support
reading the from files; then share the code.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

because we will want to support multiple public keys, and that's
easier to do in a separate function.

Should not change behavior except for order of error checks.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

The new fields `KeyPaths` and `KeyDatas` is taken directly from
`/etc/containers/policy.json` and allows users to provide multiple signature
keys to be used to verify images. Only one of the keys has to verify, thereby
this mechanism allows us to have support seamless key rotation on a registry.

This fixes containers#2319

Signed-off-by: Dan Čermák <dcermak@suse.com>
Co-authored-by: Danish Prakash <danish.prakash@suse.com>
Signed-off-by: Miloslav Trmač <mitr@redhat.com>

Add rekorPublicKeyPaths and rekorPublicKeyDatas , similar to the primary
root of trust public keys.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

This adds the ability to accept sigstore signatures signed by
any key from a set of several (huge thanks to @dcermak and
@danishprakash for doing almost all the work), and Rekor log
presence proofs signed by any key from a set of several keys.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

Signed-off-by: Miloslav Trmač <mitr@redhat.com>