public function makeAuthenticationCall()
    {
        $authResponse = $this->call('POST', [
            'grant_type' => 'client_credentials',
            'client_id' => $this->client->getClientID(),
            'client_secret' => $this->client->getClientSecret()
        ], false, ['Content-Type' => 'application/x-www-form-urlencoded'], false, false);

        if (empty($authResponse->getRaw()->access_token)) {
            throw new Exceptions\AuthenticationException;
        }

        return $authResponse;
    }