macaroons: add BakeFromRootKey function

macaroons/bake.go

@@ -0,0 +1,68 @@
+package macaroons
+
+import (
+	"bytes"
+	"fmt"
+
+	"golang.org/x/net/context"
+	"gopkg.in/macaroon-bakery.v2/bakery"
+	"gopkg.in/macaroon.v2"
+)
+
+// inMemoryRootKeyStore is a simple implementation of bakery.RootKeyStore that
+// stores a single root key in memory.
+type inMemoryRootKeyStore struct {
+	rootKey []byte
+}
+
+// A compile-time check to ensure that inMemoryRootKeyStore implements
+// bakery.RootKeyStore.
+var _ bakery.RootKeyStore = (*inMemoryRootKeyStore)(nil)
+
+// Get returns the root key for the given id. If the item is not there, it
+// returns ErrNotFound.
+func (s *inMemoryRootKeyStore) Get(_ context.Context, id []byte) ([]byte,
+	error) {
+
+	if !bytes.Equal(id, DefaultRootKeyID) {
+		return nil, bakery.ErrNotFound
+	}
+
+	return s.rootKey, nil
+}
+
+// RootKey returns the root key to be used for making a new macaroon, and an id
+// that can be used to look it up later with the Get method.
+func (s *inMemoryRootKeyStore) RootKey(context.Context) ([]byte, []byte,
+	error) {
+
+	return s.rootKey, DefaultRootKeyID, nil
+}
+
+// BakeFromRootKey creates a new macaroon that is derived from the given root
+// key and permissions.
+func BakeFromRootKey(rootKey []byte,
+	permissions []bakery.Op) (*macaroon.Macaroon, error) {
+
+	if len(rootKey) != RootKeyLen {
+		return nil, fmt.Errorf("root key must be %d bytes, is %d",
+			RootKeyLen, len(rootKey))
+	}
+
+	rootKeyStore := &inMemoryRootKeyStore{
+		rootKey: rootKey,
+	}
+
+	service, err := NewService(rootKeyStore, "lnd", false)
+	if err != nil {
+		return nil, fmt.Errorf("unable to create service: %w", err)
+	}
+
+	ctx := context.Background()
+	mac, err := service.NewMacaroon(ctx, DefaultRootKeyID, permissions...)
+	if err != nil {
+		return nil, fmt.Errorf("unable to create macaroon: %w", err)
+	}
+
+	return mac.M(), nil
+}