feat: Warn on missing signing keys when persisting challenges (#1088)

lib/store/bbolt/bbolt.go

@@ -11,10 +11,9 @@ import (
 	"go.etcd.io/bbolt"
 )
 
-// Sentinel error values used for testing and in admin-visible error messages.
+// Sentinel error value used for testing and in admin-visible error messages.
 var (
-	ErrBucketDoesNotExist = errors.New("bbolt: bucket does not exist")
-	ErrNotExists          = errors.New("bbolt: value does not exist in store")
+	ErrNotExists = errors.New("bbolt: value does not exist in store")
 )
 
 // Store implements store.Interface backed by bbolt[1].
@@ -150,6 +149,10 @@ func (s *Store) cleanup(ctx context.Context) error {
 	})
 }
 
+func (s *Store) IsPersistent() bool {
+	return true
+}
+
 func (s *Store) cleanupThread(ctx context.Context) {
 	t := time.NewTicker(time.Hour)
 	defer t.Stop()

lib/store/interface.go

@@ -37,6 +37,11 @@ type Interface interface {
 
 	// Set puts a value into the store that expires according to its expiry.
 	Set(ctx context.Context, key string, value []byte, expiry time.Duration) error
+
+	// IsPersistent returns true if this storage backend persists data across
+	// service restarts (e.g., bbolt, valkey). Returns false for volatile storage
+	// like in-memory backends.
+	IsPersistent() bool
 }
 
 func z[T any]() T { return *new(T) }
@@ -88,3 +93,7 @@ func (j *JSON[T]) Set(ctx context.Context, key string, value T, expiry time.Dura
 
 	return nil
 }
+
+func (j *JSON[T]) IsPersistent() bool {
+	return j.Underlying.IsPersistent()
+}

lib/store/memory/memory.go

@@ -48,6 +48,10 @@ func (i *impl) Set(_ context.Context, key string, value []byte, expiry time.Dura
 	return nil
 }
 
+func (i *impl) IsPersistent() bool {
+	return false
+}
+
 func (i *impl) cleanupThread(ctx context.Context) {
 	t := time.NewTicker(5 * time.Minute)
 	defer t.Stop()

lib/store/valkey/valkey.go

@@ -47,3 +47,7 @@ func (s *Store) Set(ctx context.Context, key string, value []byte, expiry time.D
 
 	return nil
 }
+
+func (s *Store) IsPersistent() bool {
+	return true
+}