code: func GetDB(c context.Context) (authdb.DB, error) {
  	if cfg := getConfig(c); cfg != nil && cfg.DBProvider != nil {
  		return cfg.DBProvider(c)
  	}
  	return authdb.ErroringDB{Error: ErrNotConfigured}, nil
  }
docs: ////////////////////////////////////////////////////////////////////////////////
  // Helpers that extract stuff from the config.
  // GetDB returns most recent snapshot of authorization database using DBProvider
  // installed in the context via 'Initialize' or 'ModifyConfig'.
  //
  // If no factory is installed, returns DB that forbids everything and logs
  // errors. It is often good enough for unit tests that do not care about
  // authorization, and still not horribly bad if accidentally used in production.