refactor: drop sigstore-protobuf-specs dependency

[woodruffw]

I come bearing gifts 🙂

This is a work in progress; it shouldn't be merged until sigstore/sigstore-python#1470 lands in a release.

Key changes:

• sigstore-protobuf-specs is entirely gone.
• I've refactored the tests to use the public OIDC beacon, and made some corresponding tweaks to the CI to use the beacon by default. This allows tests to run with 100% coverage, even on third-party PRs (like this one).

Closes #131.

[woodruffw]

Huh, no idea why this is failing in CI but not locally for me:

    @classmethod
    def from_json(cls, json: str | bytes) -> te.Self:
>       return cls.model_validate_json(json)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E       pydantic_core._pydantic_core.ValidationError: 1 validation error for TrustedRoot
E       timestampAuthorities
E         Field required [type=missing, input_value={'mediaType': 'applicatio...rjePK3/h4pygC8p7o4='}}]}, input_type=dict]
E           For further information visit https://errors.pydantic.dev/2.11/v/missing

env/lib/python3.13/site-packages/sigstore_models/_core.py:22: ValidationError
------------------------------ Captured log call -------------------------------
DEBUG    pypi_attestations._cli:_cli.py:620 Namespace(verbose=0, subcommand='verify', verification_type='attestation', identity='https://github.com/trailofbits/pypi-attestations/.github/workflows/release.yml@refs/tags/v0.0.19', staging=False, offline=True, files=[PosixPath('/home/runner/work/pypi-attestations/pypi-attestations/test/assets/pypi_attestations-0.0.19.tar.gz')])
DEBUG    sigstore._internal.tuf:tuf.py:95 TUF metadata: /home/runner/.local/share/sigstore-python/tuf/https%3A%2F%2Ftuf-repo-cdn.sigstore.dev
DEBUG    sigstore._internal.tuf:tuf.py:96 TUF targets cache: /home/runner/.cache/sigstore-python/tuf/https%3A%2F%2Ftuf-repo-cdn.sigstore.dev
WARNING  sigstore._internal.tuf:tuf.py:100 TUF repository is loaded in offline mode; updates will not be performed
DEBUG    sigstore._internal.tuf:tuf.py:130 Using unverified trusted root from cache
=============================== warnings summary ===============================

Either way this is an overly strict check in sigstore-models, so I'll fix it.

[facutuesca]

@woodruffw now that sigstore-python==4.0.0 was released, nothing is blocking this, right?

[jku]

unfortunately GitHub cached raw.githubusercontent.com quite aggressively when I last tried this -- it usually works but the error rate was still annoyingly high. This is why conformance uses the clumsy looking "git clone" approach https://github.com/sigstore/sigstore-conformance/blob/e0997c248c40ee615c1e8aa1e3ee043a62920951/test/conftest.py#L131

[jku]

an alternative (for CI only) would be to use the GH action from extremely-dangerous-public-oidc-beacon -- this is only feasible if the test suite is fast enough that it can be run with one token

[jku]

Bundle has to include a timestamp if the entry kindversion is 0.0.2 (IOW it comes from rekor2). I think including the TSA timestamp would be a good idea in general

[jku]

The more general way to say this is that the PyPI attestations should be modified so that they can include timestamps... but that should happen in another PR

[jku]

I believe the TestAttestation::test_roundtrip test is now failing (after updating some minor things) since it runs using sigstore staging and sigstore staging already defaults to rekor v2.

EDIT: confirmed: the test passes with trust_config.force_tlog_version = 1 which does the same things --rekor-version=1 does on sigstore CLI

[jku]

There is two commits for this branch in https://github.com/jku/pypi-attestations/commits/ww/drop-protobufs/

• Upgrade for sigstore-python 4.0
• forces use of rekor v2 when signing: this way we can keep the rekorv2 (and TSA) support as a separate issue
• Update README

[woodruffw]

@jku I'm probably not going to get back to this for the next week or so, so feel free to open your branch as a PR!

[facutuesca]

Closing in favor of #144