Add mutation for adding digest to image spec

pkg/handler/tuf.go

@@ -0,0 +1,17 @@
+package handler
+
+import (
+	"github.com/docker/attest/pkg/tuf"
+	"github.com/open-policy-agent/gatekeeper-external-data-provider/internal/embed"
+)
+
+func createTufClient(outputPath string) (*tuf.TufClient, error) {
+	// using oci tuf metadata and targets
+	// metadataURI := "registry-1.docker.io/docker/tuf-metadata:latest"
+	// targetsURI := "registry-1.docker.io/docker/tuf-targets"
+	// example using http tuf metadata and targets
+	metadataURI := "https://docker.github.io/tuf-staging/metadata"
+	targetsURI := "https://docker.github.io/tuf-staging/targets"
+
+	return tuf.NewTufClient(embed.StagingRoot, outputPath, metadataURI, targetsURI, tuf.NewVersionChecker())
+}