lnwallet: populate resolution blob for incoming+outgoing HTLC resolutions

In this commit, we populate the resolution blobs for the incoming and
outgoing HTLCs. We take care to populate the AuxSigDesc with the correct
information, as we need to pass along the second-level aux signature and
also sign desc along with it.

macaroons/fuzz_test.go

@@ -0,0 +1,51 @@
+package macaroons
+
+import (
+	"context"
+	"testing"
+
+	"gopkg.in/macaroon-bakery.v2/bakery"
+	"gopkg.in/macaroon.v2"
+)
+
+func FuzzUnmarshalMacaroon(f *testing.F) {
+	f.Fuzz(func(t *testing.T, data []byte) {
+		mac := &macaroon.Macaroon{}
+		_ = mac.UnmarshalBinary(data)
+	})
+}
+
+func FuzzAuthChecker(f *testing.F) {
+	rootKeyStore := bakery.NewMemRootKeyStore()
+	ctx := context.Background()
+
+	f.Fuzz(func(t *testing.T, location, entity, action, method string,
+		rootKey, id []byte) {
+
+		macService, err := NewService(
+			rootKeyStore, location, true, IPLockChecker,
+		)
+		if err != nil {
+			return
+		}
+
+		requiredPermissions := []bakery.Op{{
+			Entity: entity,
+			Action: action,
+		}}
+
+		mac, err := macaroon.New(rootKey, id, location, macaroon.V2)
+		if err != nil {
+			return
+		}
+
+		macBytes, err := mac.MarshalBinary()
+		if err != nil {
+			return
+		}
+
+		_ = macService.CheckMacAuth(
+			ctx, macBytes, requiredPermissions, method,
+		)
+	})
+}