Respect multiple TSA certificate chains in trust root

[bkabrda]

Note: right now the CI is failing, because this PR needs updating sigstore/sigstore to a version containing sigstore/sigstore#2068 which wasn't released yet. I'm not sure if the best course is to update the dependency to the specific commit or if it's better to wait until a new version is released - please let me know.

Summary

Fixes #4098 - cosign will now respect multiple TSA certificate chains provided through the trust root and will try to verify the signed timestamp with all of them (and fail if none of the TSA chains verify the signed timestamp).

Release Note

Support for multiple TSA certificate chains in the trust root was added.

Documentation

I don't believe this requires a documentation change.

[haydentherapper]

You can use the sigstore/sigstore version at the commit.

[haydentherapper]

nvm, I cut a release :) https://github.com/sigstore/sigstore/releases/tag/v1.9.4

[codecov]

Codecov Report

Attention: Patch coverage is 54.38596% with 26 lines in your changes missing coverage. Please review.

Project coverage is 36.46%. Comparing base (2ef6022) to head (6a23a02).
Report is 371 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/cosign/tsa.go	44.73%	18 Missing and 3 partials ⚠️
pkg/cosign/verify.go	86.66%	2 Missing ⚠️
cmd/cosign/cli/verify/verify.go	0.00%	1 Missing ⚠️
cmd/cosign/cli/verify/verify_attestation.go	0.00%	1 Missing ⚠️
cmd/cosign/cli/verify/verify_blob_attestation.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4174      +/-   ##
==========================================
- Coverage   40.10%   36.46%   -3.64%     
==========================================
  Files         155      210      +55     
  Lines       10044    13762    +3718     
==========================================
+ Hits         4028     5019     +991     
- Misses       5530     8120    +2590     
- Partials      486      623     +137     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[bkabrda]

@haydentherapper thanks for the quick release of the sigstore library. I updated the PR to incorporate that, but I noticed that one e2e test is failing; it looks like it might be related to my change, so I'll try to take a look at it later today to see what's going wrong.

[bkabrda]

Ok, I understand what's going wrong; in the "nonstandard key names with valid usage", it is assumed that even if multiple targets with "Usage: TSA" are used, they are still just parts of one certificate chain, but my code change expects these to be full certificate chains and therefore it fails on parsing them as such.

Even though I dislike the behavior, I think technically my change is breaking it and so probably shouldn't be merged... WDYT @haydentherapper? I currently don't see a fully backwards compatible way of making this work with the "old-style" tuf targets and so probably the best way to go would be to wait for the trusted_root.json support to get merged.