Support Kerberos for the HTTP classes

It would be nice if the HTTP access in Qt could use Kerberos authentication as well as the currently supported NTLM scheme.

Alternatively, allow an implementation of Kerberos authentication to be added by a subclasses. If the following functions would be moved from the QAuthenticatorPrivate and made virtual , then this could be reimplement added without changing the QHttp/QAuthenticator code itself:

void QAuthenticatorPrivate::parseHttpResponse(const QHttpResponseHeader &header, bool isProxy)
QByteArray QAuthenticatorPrivate::calculateResponse(const QByteArray &requestMethod, const QByteArray &path)

QAuthenticator is a value type so adding virtual functions or signals is not possible, but a new class QAuthenticatorResponseHandler could be created with a virtual interface, and set as a value on the QAuthenticator.