QNetworkAccessManager *networkManager = new QNetworkAccessManager(this);

QByteArray postData;
QSslConfiguration config;
QString pemfile("path/to/cl_signed.pem");
QFile file(pemfile);
if(!file.exists()) {
    qWarning("Filename doent exists");
}
if(!file.open(QIODevice::ReadOnly)) {
    qWarning("Cannot open filename %s.", qPrintable(pemfile));
}  
QByteArray data_cert =file.readAll() ;
QSslCertificate sslcert(data_cert, QSsl::Pem);
config.setLocalCertificate(sslcert);
if(sslcert.isNull()) {
    qWarning("The certificate has no content.");
}
QByteArray keyData;
const QSslKey sslPrivateKey (keyData, QSsl::Rsa, QSsl::Pem, QSsl::PrivateKey, "privatekey");
config.setPrivateKey(sslPrivateKey);
QUrl url("http:...................../oauth2/v1/token?");
QNetworkRequest request(url);
postData.append("param1");
postData.append("param2");
postData.append("param3");
postData.append(param4");
request.setHeader(QNetworkRequest::ContentTypeHeader,"application/x-www-form-urlencoded");
networkManager->post(request,postData);
QNetworkAccessManager mgr;
QObject::connect(&mgr, SIGNAL(finished(QNetworkReply*)), SLOT(quit()));
QNetworkReply *reply = mgr.get(request);
if (reply->error() == QNetworkReply::NoError) 
 {
    QString strReply = (QString)reply->readAll();
    qDebug() << "Response:" << strReply;
    QJsonDocument jsonResponse = QJsonDocument::fromJson(strReply.toUtf8());
    QJsonObject jsonObj = jsonResponse.object();
    qDebug() << "result:" << jsonObj["result"].toInt();
    delete reply;
 }
else
 {
    qDebug() << "Failure" 
    delete reply;
 }