Chains should stop signing artifacts type-hinted in pipelines

Feature request

Chains uses type hinting to identify the artifacts that might be produced in a pipeline. Even if it was possible for Chains to identify whether the artifact was produced in the pipeline, Chains knows nothing about the artifact.

Since Chains knows nothing about, a consumer of the signed artifacts would not have any additional hardened security posture by requiring this Chains produced signature. At best, consumers would know to effectively ignore the signature. At worst, consumers would put additional trust in the signature which can be easily applied to untrusted artifacts.

If signatures are just used to ensure that artifacts are not mutated from when they were produced, the generated SLSA provenance can be used as this also is created with the Chains identity.

Use case

Consumers of signatures might want to use signature verification as a means to hardening a software supply chain. Therefore, signatures should have a specific meaning which maps to a supply chain hardening pattern.

The issue does not name any files, tests, or entry points. Start by tracing how Chains discovers type-hinted pipeline artifacts and applies signatures, then clarify the intended behavior and affected verification or provenance tests with maintainers. Done should mean type-hinted artifacts are not signed unless Chains can establish their provenance.