Add support to attestation command for more predicate types.

Before, we required all attestations have predicateType
https://slsa.dev/provenance/v1. This allows you to use other predicate
types, and adds the ability to filter responses from the API for a
particular predicate type.

Signed-off-by: Zach Steindler <steiza@github.com>

pkg/cmd/attestation/download/download.go

@@ -102,6 +102,7 @@ func NewDownloadCmd(f *cmdutil.Factory, runF func(*Options) error) *cobra.Comman
 	downloadCmd.Flags().StringVarP(&opts.Repo, "repo", "R", "", "Repository name in the format <owner>/<repo>")
 	downloadCmd.MarkFlagsMutuallyExclusive("owner", "repo")
 	downloadCmd.MarkFlagsOneRequired("owner", "repo")
+	downloadCmd.Flags().StringVarP(&opts.PredicateType, "predicate-type", "", "", "Filter attestations by provided predicate type")
 	cmdutil.StringEnumFlag(downloadCmd, &opts.DigestAlgorithm, "digest-alg", "d", "sha256", []string{"sha256", "sha512"}, "The algorithm used to compute a digest of the artifact")
 	downloadCmd.Flags().IntVarP(&opts.Limit, "limit", "L", api.DefaultLimit, "Maximum number of attestations to fetch")
 
@@ -132,6 +133,17 @@ func runDownload(opts *Options) error {
 		return fmt.Errorf("failed to fetch attestations: %v", err)
 	}
 
+	// Apply predicate type filter to returned attestations
+	if opts.PredicateType != "" {
+		filteredAttestations := verification.FilterAttestations(opts.PredicateType, attestations)
+
+		if len(filteredAttestations) == 0 {
+			return fmt.Errorf("no attestations found with predicate type: %s", opts.PredicateType)
+		}
+
+		attestations = filteredAttestations
+	}
+
 	metadataFilePath, err := opts.Store.createMetadataFile(artifact.DigestWithAlg(), attestations)
 	if err != nil {
 		return fmt.Errorf("failed to write attestation: %v", err)

pkg/cmd/attestation/download/options.go

@@ -22,6 +22,7 @@ type Options struct {
 	Store           MetadataStore
 	OCIClient       oci.Client
 	Owner           string
+	PredicateType   string
 	Repo            string
 }
 

pkg/cmd/attestation/verification/attestation.go

@@ -2,6 +2,7 @@ package verification
 
 import (
 	"bufio"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"os"
@@ -113,3 +114,27 @@ func GetRemoteAttestations(c FetchAttestationsConfig) ([]*api.Attestation, error
 	}
 	return nil, fmt.Errorf("owner or repo must be provided")
 }
+
+type DssePayload struct {
+	PredicateType string `json:"predicateType"`
+}
+
+func FilterAttestations(predicateType string, attestations []*api.Attestation) []*api.Attestation {
+	filteredAttestations := []*api.Attestation{}
+
+	for _, each := range attestations {
+		dsseEnvelope := each.Bundle.GetDsseEnvelope()
+		if dsseEnvelope != nil {
+			var dssePayload DssePayload
+			if err := json.Unmarshal([]byte(dsseEnvelope.Payload), &dssePayload); err != nil {
+				// Don't fail just because a single entry can't be unmarshalled
+				continue
+			}
+			if dssePayload.PredicateType == predicateType {
+				filteredAttestations = append(filteredAttestations, each)
+			}
+		}
+	}
+
+	return filteredAttestations
+}

pkg/cmd/attestation/verify/options.go

@@ -21,6 +21,7 @@ type Options struct {
 	NoPublicGood         bool
 	OIDCIssuer           string
 	Owner                string
+	PredicateType        string
 	Repo                 string
 	SAN                  string
 	SANRegex             string

pkg/cmd/attestation/verify/policy.go

@@ -12,7 +12,6 @@ import (
 
 const (
 	GitHubOIDCIssuer  = "https://token.actions.githubusercontent.com"
-	SLSAPredicateType = "https://slsa.dev/provenance/v1"
 	// represents the GitHub hosted runner in the certificate RunnerEnvironment extension
 	GitHubRunner = "github-hosted"
 )

pkg/cmd/attestation/verify/verify.go

@@ -1,7 +1,6 @@
 package verify
 
 import (
-	// "encoding/json"
 	"errors"
 	"fmt"
 
@@ -17,8 +16,6 @@ import (
 	"github.com/spf13/cobra"
 )
 
-var ErrNoMatchingSLSAPredicate = fmt.Errorf("the attestation does not have the expected SLSA predicate type: %s", SLSAPredicateType)
-
 func NewVerifyCmd(f *cmdutil.Factory, runF func(*Options) error) *cobra.Command {
 	opts := &Options{}
 	verifyCmd := &cobra.Command{
@@ -120,6 +117,7 @@ func NewVerifyCmd(f *cmdutil.Factory, runF func(*Options) error) *cobra.Command
 	verifyCmd.Flags().StringVarP(&opts.Repo, "repo", "R", "", "Repository name in the format <owner>/<repo>")
 	verifyCmd.MarkFlagsMutuallyExclusive("owner", "repo")
 	verifyCmd.MarkFlagsOneRequired("owner", "repo")
+	verifyCmd.Flags().StringVarP(&opts.PredicateType, "predicate-type", "", "", "Filter attestations by provided predicate type")
 	verifyCmd.Flags().BoolVarP(&opts.NoPublicGood, "no-public-good", "", false, "Only verify attestations signed with GitHub's Sigstore instance")
 	verifyCmd.Flags().StringVarP(&opts.CustomTrustedRoot, "custom-trusted-root", "", "", "Path to a custom trustedroot.json file to use for verification")
 	verifyCmd.Flags().IntVarP(&opts.Limit, "limit", "L", api.DefaultLimit, "Maximum number of attestations to fetch")
@@ -158,6 +156,17 @@ func runVerify(opts *Options) error {
 		return fmt.Errorf("failed to fetch attestations for subject: %s", artifact.DigestWithAlg())
 	}
 
+	// Apply predicate type filter to returned attestations
+	if opts.PredicateType != "" {
+		filteredAttestations := verification.FilterAttestations(opts.PredicateType, attestations)
+
+		if len(filteredAttestations) == 0 {
+			return fmt.Errorf("no attestations found with predicate type: %s", opts.PredicateType)
+		}
+
+		attestations = filteredAttestations
+	}
+
 	policy, err := buildVerifyPolicy(opts, *artifact)
 	if err != nil {
 		return fmt.Errorf("failed to build policy: %v", err)
@@ -183,11 +192,6 @@ func runVerify(opts *Options) error {
 		"Successfully verified all attestations against Sigstore!\n",
 	))
 
-	// Try verifying the attestation's predicate type against the expect SLSA predicate type
-	if err = verifySLSAPredicateType(opts.Logger, sigstoreRes.VerifyResults); err != nil {
-		return fmt.Errorf("at least one attestation failed to verify predicate type verification: %v", err)
-	}
-
 	opts.Logger.VerbosePrint(opts.Logger.ColorScheme.Green("Successfully verified the SLSA predicate type of all attestations!\n"))
 
 	opts.Logger.Println(opts.Logger.ColorScheme.Green("All attestations have been successfully verified!"))
@@ -202,15 +206,3 @@ func runVerify(opts *Options) error {
 	// All attestations passed verification and policy evaluation
 	return nil
 }
-
-func verifySLSAPredicateType(logger *io.Handler, apr []*verification.AttestationProcessingResult) error {
-	logger.VerbosePrint("Evaluating attestations have valid SLSA predicate type")
-
-	for _, result := range apr {
-		if result.VerificationResult.Statement.PredicateType != SLSAPredicateType {
-			return ErrNoMatchingSLSAPredicate
-		}
-	}
-
-	return nil
-}

pkg/cmd/attestation/verify/verify_test.go

@@ -19,9 +19,6 @@ import (
 	"github.com/cli/cli/v2/pkg/iostreams"
 	"github.com/stretchr/testify/assert"
 
-	"github.com/in-toto/in-toto-golang/in_toto"
-	"github.com/sigstore/sigstore-go/pkg/verify"
-
 	"github.com/stretchr/testify/require"
 )
 
@@ -382,20 +379,3 @@ func TestRunVerify(t *testing.T) {
 		require.Error(t, runVerify(&customOpts))
 	})
 }
-
-func TestVerifySLSAPredicateType_InvalidPredicate(t *testing.T) {
-	statement := &in_toto.Statement{}
-	statement.PredicateType = "some-other-predicate-type"
-
-	apr := []*verification.AttestationProcessingResult{
-		{
-			VerificationResult: &verify.VerificationResult{
-				Statement: statement,
-			},
-		},
-	}
-
-	err := verifySLSAPredicateType(io.NewTestHandler(), apr)
-	require.Error(t, err)
-	require.ErrorIs(t, err, ErrNoMatchingSLSAPredicate)
-}