public function getOrFetchAccessToken(
        FetchAuthTokenInterface $fetchAuthTokenInterface,
        callable $httpHandler = null
    ) {
        if ($this->shouldFetchAccessToken($fetchAuthTokenInterface)) {
            return $fetchAuthTokenInterface->fetchAuthToken($httpHandler)
            ['access_token'];
        }

        return $fetchAuthTokenInterface->getLastReceivedToken()['access_token'];
    }