Correct format for HTTP POST using QNetworkRequest

This is not the right way to write your HTTP request. The following piece of code is more correct :

connect(m_qnam, SIGNAL(finished(QNetworkReply*)), this, SLOT(handleNetworkData(QNetworkReply*)));
connect(m_qnam,SIGNAL(sslErrors(QNetworkReply*,QList<QSslError>)), this, SLOT(handleSSLErrors(QNetworkReply*)));

// Build your JSON string as usual
QByteArray jsonString = "{\"method\":\"AuthenticatePlain\",\"loginName\":\"[email protected]\",\"password\":\"mypass\"}";

// For your "Content-Length" header
QByteArray postDataSize = QByteArray::number(jsonString.size());

// Time for building your request
QUrl serviceURL("https://www.superService.com/api/1.7/ssapi.asmx");
QNetworkRequest request(serviceURL);

// Add the headers specifying their names and their values with the following method : void QNetworkRequest::setRawHeader(const QByteArray & headerName, const QByteArray & headerValue);
request.setRawHeader("User-Agent", "My app name v0.1");
request.setRawHeader("X-Custom-User-Agent", "My app name v0.1");
request.setRawHeader("Content-Type", "application/json");
request.setRawHeader("Content-Length", postDataSize);

// Use QNetworkReply * QNetworkAccessManager::post(const QNetworkRequest & request, const QByteArray & data); to send your request. Qt will rearrange everything correctly.
QNetworkReply * reply = m_qnam->post(request, jsonString);