Update cosign to v2.0.2

[developer-guy]

Abstract

OCI Reference Types has made a tremendous effort to make the relationships easier between the OCI Image and its materials such as SBOMs, attestations, vuln scan results, and build information. go-containerregistry is working on adding support for the Referrers API. Once this has landed, cosign plans to change how to store signatures. It will also affect the Flux projects since they use cosign under the hood to verify the signatures of the OCI Artifacts.

Helper Resources

• Also, thanks to @dlorenc for writing an introductory guide for OCI Reference Types.
• Another excellent presentation by @sudobmitch about Referrers API

/cc @souleb @stefanprodan @Dentrax

[developer-guy]

https://github.com/sigstore/cosign/pull/2684

[developer-guy]

https://www.chainguard.dev/unchained/building-towards-oci-v1-1-support-in-cosign

[souleb]

Thanks @developer-guy, after reading the PRs, my understand is that with the fall back for 1.0 registries there is nothing to do in Flux.

[stefanprodan]

We need to update SC to latest cosign as rekor has a CVE. This is not just a simple bump in go.mod as cosign v2 comes with many breaking changes. Can someone please look into it?

[makkes]

related: #1083