QSslConfiguration::setLocalCertificate only accepts one single certificate. But aduring client authentication, the client must present his certificate including the full chain of intermediate certificates up to (and including) the root.
The actual implementation does not work, if the server only installs the CA-root-certificate, but not the issuing certificates, and the CA uses issuing certificate (as e.g. SwissSign).
void QSslCertificatePrivate::init(const QByteArray &data, QSsl::EncodingFormat format) ignores all certificats exept the first one and QSslConfiguration::setLocalCertificate does not accept a list. Both should be corrected.
The same problem exists in Apple/Safari, b.t.w.