chore(deps): update dependency cosign to v2.6.0

[renovate]

This PR contains the following updates:

Package	Update	Change
cosign	minor	v2.5.3 -> v2.6.0

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Release Notes

sigstore/cosign (cosign)

v2.6.0

Compare Source

v2.6.0 introduces a number of new features, including:

• Signing an in-toto statement rather than Cosign constructing one from a predicate, along with verifying a statement's subject using a digest and digest algorithm rather than providing a file reference (#​4306)
• Uploading a signature and its verification material (a "bundle") as an OCI Image 1.1 referring artifact, completing #​3927 (#​4316)
• Providing service URLs for signing and attesting using a SigningConfig. Note that this is required when using a Rekor v2 instance (#​4319)

Example generation and verification of a signed in-toto statement:

cosign attest-blob --new-bundle-format=true --bundle="digest-key-test.sigstore.json" --key="cosign.key" --statement="../sigstore-go/examples/sigstore-go-signing/intoto.txt"
cosign verify-blob-attestation --bundle="digest-key-test.sigstore.json" --key=cosign.pub --type=unused --digest="b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9" --digestAlg="sha256"

Example container signing and verification using the new bundle format and referring artifacts:

cosign sign --new-bundle-format=true ghcr.io/user/alpine@sha256:a19367999603840546b8612572e338ec076c6d1f2fec61760a9e11410f546733
cosign verify --new-bundle-format=true ghcr.io/user/alpine@sha256:a19367999603840546b8612572e338ec076c6d1f2fec61760a9e11410f546733

Example usage of a signing config provided by the public good instance's TUF repository:

cosign sign-blob --use-signing-config --bundle sigstore.json README.md
cosign verify-blob --new-bundle-format --bundle sigstore.json --certificate-identity $EMAIL --certificate-oidc-issuer $ISSUER --use-signed-timestamps README.md

v2.6.0 leverages sigstore-go's signing and verification APIs gated behind these new flags. In an upcoming major release, we will be
updating Cosign to default to producing and consuming bundles to align with all other Sigstore SDKs.

Features

• Add to attest-blob the ability to supply a complete in-toto statement, and add to verify-blob-attestation the ability to verify with just a digest (#​4306)
• Have cosign sign support bundle format (#​4316)
• Add support for SigningConfig for sign-blob/attest-blob, support Rekor v2 (#​4319)
• Add support for SigningConfig in sign/attest (#​4371)
• Support self-managed keys when signing with sigstore-go (#​4368)
• Don't require timestamps when verifying with a key (#​4337)
• Don't load content from TUF if trusted root path is specified (#​4347)
• Add a terminal spinner while signing with sigstore-go (#​4402)
• Require exclusively a SigningConfig or service URLs when signing (#​4403)
• Remove SHA256 assumption in sign-blob/verify-blob (#​4050)
• Bump sigstore-go, support alternative hash algorithms with keys (#​4386)

Breaking API Changes

• sign.SignerFromKeyOpts no longer generates a key. Instead, it returns whether or not the client needs to generate a key, and if so, clients
  should call sign.KeylessSigner. This allows clients to more easily manage key generation.

Bug Fixes

• Verify subject with bundle only when checking claims (#​4320)
• Fixes to cosign sign / verify for the new bundle format (#​4346)

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