allow shutting down jwk cache (#1457)

Author: adam-bates

jwk/cache.go

@@ -223,6 +223,10 @@ func (c *Cache) Unregister(ctx context.Context, u string) error {
 	return c.ctrl.Remove(ctx, u)
 }
 
+func (c *Cache) Shutdown(ctx context.Context) error {
+	return c.ctrl.ShutdownContext(ctx)
+}
+
 // CachedSet is a thin shim over jwk.Cache that allows the user to cloak
 // jwk.Cache as if it's a `jwk.Set`. Behind the scenes, the `jwk.Set` is
 // retrieved from the `jwk.Cache` for every operation.