Honor custom signer identities during chain evaluation - #439
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Closes #436.
Summary
--expected-issuerand--expected-sanwhen the GitHub backend evaluates prior attestations.Problem
sourcetool.Newalready creates a verifier from the configured expected identity for its top-level attester. However,Backend.GetBranchControlsAtCommitcreates another attester withattest.GetDefaultVerifier().That second verifier rejects otherwise valid prior attestations signed by a caller's configured workflow identity. As a result, provenance and VSA controls do not carry forward during chain evaluation, and the computed SLSA Source level can remain at L1.
Implementation
The GitHub backend constructor now accepts optional backend configuration while retaining its existing default behavior.
sourcetool.Newbuilds one verifier and passes it to both the top-level attester and the GitHub backend. Chain evaluation therefore uses the same issuer, SAN, and alternate-SAN policy as direct attestation verification.This does not broaden trust by default. Existing
github.New(options)callers still receiveattest.GetDefaultVerifier(), and a nil verifier option leaves that default intact.Validation
go test ./...go test -race -count=1 ./pkg/sourcetool/... ./pkg/attest/...go vet ./...go run github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.12.0 run ./...git diff --check