feat(notation): Image verifier (#5)

* feat: Notation Image verifier

* chore: updates

* fix: MaxSigAttempts parameter

* chore: test config loading

* fix: test was missing parameter

admissionctrl/notation/notation.go

@@ -0,0 +1,94 @@
+package notation
+
+import (
+	"context"
+	"encoding/json"
+	"os"
+
+	"github.com/hashicorp/go-hclog"
+	_ "github.com/notaryproject/notation-core-go/signature/cose"
+	_ "github.com/notaryproject/notation-core-go/signature/jws"
+	"github.com/notaryproject/notation-go"
+	"github.com/notaryproject/notation-go/registry"
+	"github.com/notaryproject/notation-go/verifier"
+	"github.com/notaryproject/notation-go/verifier/trustpolicy"
+	"github.com/notaryproject/notation-go/verifier/truststore"
+	"oras.land/oras-go/v2/registry/remote"
+)
+
+type ImageVerifier interface {
+	VerifyImage(ctx context.Context, imageReference string) error
+}
+
+// notationImageVerifier is a struct that represents an image verifier.
+type notationImageVerifier struct {
+	verifier             notation.Verifier
+	repoPlainHTTP        bool
+	maxSignatureAttempts int
+	logger               hclog.Logger
+}
+
+// LoadTrustPolicyDocument loads a trust policy document from the given path.
+// It returns the trust policy document or an error if the document cannot be loaded.
+func LoadTrustPolicyDocument(path string) (*trustpolicy.Document, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	doc := &trustpolicy.Document{}
+	err = json.Unmarshal(data, doc)
+	if err != nil {
+		return nil, err
+	}
+	return doc, nil
+}
+
+// NewImageVerifier creates a new ImageVerifier instance with the given trust policy, trust store, and repoPlainHTTP flag.
+// It returns the ImageVerifier instance or an error if the verifier cannot be created.
+func NewImageVerifier(policy *trustpolicy.Document, truststore truststore.X509TrustStore, repoPlainHTTP bool, maxSignatureAttempts int, logger hclog.Logger) (ImageVerifier, error) {
+
+	verifier, err := verifier.New(policy, truststore, nil)
+	if err != nil {
+		return nil, err
+	}
+	return &notationImageVerifier{
+		verifier:             verifier,
+		repoPlainHTTP:        repoPlainHTTP,
+		logger:               logger,
+		maxSignatureAttempts: maxSignatureAttempts,
+	}, nil
+
+}
+
+// VerifyImage verifies the image with the given image reference.
+// It returns an error if the verification fails.
+func (iv *notationImageVerifier) VerifyImage(ctx context.Context, imageReference string) error {
+
+	// derived from https://pkg.go.dev/github.com/notaryproject/[email protected]#example-package-RemoteVerify
+
+	remoteRepo, err := remote.NewRepository(imageReference)
+	remoteRepo.PlainHTTP = iv.repoPlainHTTP
+	if err != nil {
+		iv.logger.Debug("Remote repository creation failed", "err", err, "reference", imageReference)
+		return err
+	}
+	repo := registry.NewRepository(remoteRepo)
+
+	// verifyOptions is an example of notation.VerifyOptions.
+	verifyOptions := notation.VerifyOptions{
+		ArtifactReference:    imageReference,
+		MaxSignatureAttempts: iv.maxSignatureAttempts,
+	}
+
+	// remote verify core process
+	// upon successful verification, the target manifest descriptor
+	// and signature verification outcome are returned.
+	targetDesc, _, err := notation.Verify(ctx, iv.verifier, repo, verifyOptions)
+	if err != nil {
+		iv.logger.Debug("Notation verify failed", "err", err, "reference", imageReference)
+		return err
+	}
+
+	iv.logger.Debug("Notation verify succeeded", "reference", imageReference, "digest", targetDesc.Digest, "size", targetDesc.Size, "mediaType", targetDesc.MediaType)
+	return nil
+}