Add option to disable signatures

Add option for specifying trust key for signing schema1 manifests.
Since schema1 signature key identifiers are not verified anywhere and deprecated, storing signatures is no longer a requirement.
Furthermore in schema2 there is no signature, requiring the registry to already add signatures to generated schema1 manifests.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

registry/storage/registry.go

@@ -6,6 +6,7 @@ import (
 	"github.com/docker/distribution/reference"
 	"github.com/docker/distribution/registry/storage/cache"
 	storagedriver "github.com/docker/distribution/registry/storage/driver"
+	"github.com/docker/libtrust"
 )
 
 // registry is the top-level implementation of Registry for use in the storage
@@ -17,6 +18,8 @@ type registry struct {
 	blobDescriptorCacheProvider cache.BlobDescriptorCacheProvider
 	deleteEnabled               bool
 	resumableDigestEnabled      bool
+	schema1SignaturesEnabled    bool
+	schema1SigningKey           libtrust.PrivateKey
 }
 
 // RegistryOption is the type used for functional options for NewRegistry.
@@ -43,6 +46,24 @@ func DisableDigestResumption(registry *registry) error {
 	return nil
 }
 
+// DisableSchema1Signatures is a functional option for NewRegistry. It disables
+// signature storage and ensures all schema1 manifests will only be returned
+// with a signature from a provided signing key.
+func DisableSchema1Signatures(registry *registry) error {
+	registry.schema1SignaturesEnabled = false
+	return nil
+}
+
+// Schema1SigningKey returns a functional option for NewRegistry. It sets the
+// signing key for adding a signature to all schema1 manifests. This should be
+// used in conjunction with disabling signature store.
+func Schema1SigningKey(key libtrust.PrivateKey) RegistryOption {
+	return func(registry *registry) error {
+		registry.schema1SigningKey = key
+		return nil
+	}
+}
+
 // BlobDescriptorCacheProvider returns a functional option for
 // NewRegistry. It creates a cached blob statter for use by the
 // registry.
@@ -85,8 +106,9 @@ func NewRegistry(ctx context.Context, driver storagedriver.StorageDriver, option
 			statter: statter,
 			pathFn:  bs.path,
 		},
-		statter:                statter,
-		resumableDigestEnabled: true,
+		statter:                  statter,
+		resumableDigestEnabled:   true,
+		schema1SignaturesEnabled: true,
 	}
 
 	for _, option := range options {