public function getAuthenticationURL($responseType = 'code', $state = null)
    {
        $httpQueryParameters = [
            'client_id' => $this->clientId,
            'response_type' => $responseType,
            'state' => $state,
        ];

        $httpQueryParameters = http_build_query($httpQueryParameters);

        return self::AUTHORIZATION_ENDPOINT . '?' . $httpQueryParameters;
    }