feat: add verification required log

Signed-off-by: Junjie Gao <junjiegao@microsoft.com>

notation.go

@@ -13,6 +13,7 @@ import (
 	"time"
 
 	"github.com/notaryproject/notation-core-go/signature"
+	"github.com/notaryproject/notation-go/log"
 	"github.com/notaryproject/notation-go/registry"
 	"github.com/notaryproject/notation-go/verifier/trustpolicy"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
@@ -186,6 +187,8 @@ func Verify(ctx context.Context, verifier Verifier, repo registry.Repository, re
 	var verificationOutcomes []*VerificationOutcome
 	errExceededMaxVerificationLimit := ErrorVerificationFailed{Msg: fmt.Sprintf("total number of signatures associated with an artifact should be less than: %d", remoteOpts.MaxSignatureAttempts)}
 	numOfSignatureProcessed := 0
+
+	logger := log.GetLogger(ctx)
 	err = repo.ListSignatures(ctx, artifactDescriptor, func(signatureManifests []ocispec.Descriptor) error {
 		// process signatures
 		for _, sigManifestDesc := range signatureManifests {
@@ -203,6 +206,18 @@ func Verify(ctx context.Context, verifier Verifier, repo registry.Repository, re
 
 			// verify each signature
 			outcome, err := verifier.Verify(ctx, artifactDescriptor, sigBlob, opts)
+			// process verification items
+			for _, result := range outcome.VerificationResults {
+				if result.Error == nil {
+					continue
+				}
+				switch result.Action {
+				case trustpolicy.ActionLog:
+					logger.Warnf("verification failed on %v validation for signature %v but set to pass by verification action \"logged\". Reason: %v", result.Type, sigManifestDesc.Digest, result.Error)
+				case trustpolicy.ActionEnforce:
+					logger.Errorf("verification failed on %v validation for signature %v. Reason: %v", result.Type, sigManifestDesc.Digest, result.Error)
+				}
+			}
 			if err != nil {
 				if outcome == nil {
 					// TODO: log fatal error