code: func GetRegistry(r *http.Request) *Registry {
  	var ctx = r.Context()
  	registry := ctx.Value(registryKey)
  	if registry != nil {
  		return registry.(*Registry)
  	}
  	newRegistry := &Registry{
  		request:  r,
  		sessions: make(map[string]sessionInfo),
  	}
  	*r = *r.WithContext(context.WithValue(ctx, registryKey, newRegistry))
  	return newRegistry
  }
docs: // GetRegistry returns a registry instance for the current request.