protected function fetchRequestToken()
    {
        // Fetching a new request token. Remove any old access tokens.
        $this->storage->delete(static::BIB_ACCESS_TOKEN);
        // Fetch a request token.
        $token = $this->consumer->getRequestToken();
        // Persist the token to storage.
        $this->storage->set(static::BIB_REQUEST_TOKEN, $token);

        return $this;
    }