Add CertExtensions func to extract all extensions (sigstore#1515)

* Add CertExtensions func to extract all extensions

Signed-off-by: Christian Kotzbauer <git@ckotzbauer.de>

* Renamed issuer to oidcIssuer

Signed-off-by: Christian Kotzbauer <git@ckotzbauer.de>

pkg/signature/keys.go

@@ -43,6 +43,25 @@ import (
 	_ "github.com/sigstore/sigstore/pkg/signature/kms/hashivault"
 )
 
+var (
+	// Fulcio cert-extensions, documented here: https://github.com/sigstore/fulcio/blob/main/docs/oid-info.md
+	CertExtensionOIDCIssuer               = "1.3.6.1.4.1.57264.1.1"
+	CertExtensionGithubWorkflowTrigger    = "1.3.6.1.4.1.57264.1.2"
+	CertExtensionGithubWorkflowSha        = "1.3.6.1.4.1.57264.1.3"
+	CertExtensionGithubWorkflowName       = "1.3.6.1.4.1.57264.1.4"
+	CertExtensionGithubWorkflowRepository = "1.3.6.1.4.1.57264.1.5"
+	CertExtensionGithubWorkflowRef        = "1.3.6.1.4.1.57264.1.6"
+
+	CertExtensionMap = map[string]string{
+		CertExtensionOIDCIssuer:               "oidcIssuer",
+		CertExtensionGithubWorkflowTrigger:    "githubWorkflowTrigger",
+		CertExtensionGithubWorkflowSha:        "githubWorkflowSha",
+		CertExtensionGithubWorkflowName:       "githubWorkflowName",
+		CertExtensionGithubWorkflowRepository: "githubWorkflowRepository",
+		CertExtensionGithubWorkflowRef:        "githubWorkflowRef",
+	}
+)
+
 // LoadPublicKey is a wrapper for VerifierForKeyRef, hardcoding SHA256 as the hash algorithm
 func LoadPublicKey(ctx context.Context, keyRef string) (verifier signature.Verifier, err error) {
 	return VerifierForKeyRef(ctx, keyRef, crypto.SHA256)
@@ -243,9 +262,22 @@ func CertSubject(c *x509.Certificate) string {
 
 func CertIssuerExtension(cert *x509.Certificate) string {
 	for _, ext := range cert.Extensions {
-		if ext.Id.String() == "1.3.6.1.4.1.57264.1.1" {
+		if ext.Id.String() == CertExtensionOIDCIssuer {
 			return string(ext.Value)
 		}
 	}
 	return ""
 }
+
+func CertExtensions(cert *x509.Certificate) map[string]string {
+	extensions := map[string]string{}
+	for _, ext := range cert.Extensions {
+		readableName, ok := CertExtensionMap[ext.Id.String()]
+		if ok {
+			extensions[readableName] = string(ext.Value)
+		} else {
+			extensions[ext.Id.String()] = string(ext.Value)
+		}
+	}
+	return extensions
+}

pkg/signature/keys_test.go

@@ -16,6 +16,9 @@ package signature
 
 import (
 	"context"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/asn1"
 	"os"
 	"testing"
 
@@ -110,3 +113,41 @@ func pass(s string) cosign.PassFunc {
 		return []byte(s), nil
 	}
 }
+
+func createCert(t *testing.T) *x509.Certificate {
+	t.Helper()
+	return &x509.Certificate{
+		Extensions: []pkix.Extension{
+			{Id: asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 57264, 1, 1}, Value: []byte("myIssuer")},
+			{Id: asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 57264, 1, 4}, Value: []byte("myWorkflowName")},
+			{Id: asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 57264, 1, 6}, Value: []byte("myWorkflowRef")},
+			{Id: asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 57264, 1, 42}, Value: []byte("myCustomExtension")},
+		},
+	}
+}
+
+func TestCertExtensions(t *testing.T) {
+	t.Parallel()
+	cert := createCert(t)
+	exts := CertExtensions(cert)
+
+	if len(exts) != 4 {
+		t.Fatalf("Unexpected extension-count: %v", len(exts))
+	}
+
+	if val, ok := exts["oidcIssuer"]; !ok || val != "myIssuer" {
+		t.Fatal("CertExtension does not extract field 'oidcIssuer' correctly")
+	}
+
+	if val, ok := exts["githubWorkflowName"]; !ok || val != "myWorkflowName" {
+		t.Fatal("CertExtension does not extract field 'githubWorkflowName' correctly")
+	}
+
+	if val, ok := exts["githubWorkflowRef"]; !ok || val != "myWorkflowRef" {
+		t.Fatal("CertExtension does not extract field 'githubWorkflowRef' correctly")
+	}
+
+	if val, ok := exts["1.3.6.1.4.1.57264.1.42"]; !ok || val != "myCustomExtension" {
+		t.Fatal("CertExtension does not extract field '1.3.6.1.4.1.57264.1.42' correctly")
+	}
+}