Add support for image-indexes

[roeishuster]

Is your feature request related to a problem?

Currently, we cannot sign image indexes, and we use image indexes in some scenarios.
Without singing them, we can't fully run notation with ratify as we cannot validate this kind of artifact.

What solution do you propose?

To be able to sign image-indexes too, same as regular images.

What alternatives have you considered?

Excluding specific pods/namespaces that use image indexes or forcing the use of images only in our environment which is not good enough.

Any additional context?

No response

[FeynmanZhou]

Hi @roeishuster , do you expect to sign both the image index and its child image manifest or sign the image index only? Is it a scenario of signing and verifying multi-arch image? It would be good to elaborate more on your feature request. Thanks

[roeishuster]

@FeynmanZhou What we see in our pods verification is the image index only, so we think it would be sufficient to be able to sign the index only.

[FeynmanZhou]

Hi @roeishuster , notation should be able to sign the image index only. Have you ever signed it before verifying with Ratify? Is there any specific errors?

[roeishuster]

@FeynmanZhou it looks like you are right, we can close this :)