QT5.9.1， 自编译的qmqtt。
设置如下：
QSslSocket ssl_socket;
ssl_socket.setPrivateKey(CERTS_ROOT_FILE + QString( "/qt/client.key"));
ssl_socket.setLocalCertificate(CERTS_ROOT_FILE + QString( "/qt/client.crt"));
ssl_socket.setPeerVerifyMode(QSslSocket::VerifyPeer);//双向验证
QSslConfiguration ssl_config=QSslConfiguration::defaultConfiguration();
ssl_config.setCaCertificates(QSslCertificate::fromPath(CERTS_ROOT_FILE + QString( "/qt/rootCA.pem")));
ssl_config.setPrivateKey(ssl_socket.privateKey());
ssl_config.setLocalCertificate(ssl_socket.localCertificate());
ssl_config.setPeerVerifyMode(QSslSocket::VerifyPeer);
ssl_config.setPeerVerifyDepth(1);
ssl_config.setProtocol(QSsl::TlsV1_2);
m_client = new QMQTT::Client(hostName, hostPort, ssl_config);
证书使用的是QT example里自带的，MQTT.FX-1.3.1用此证书可以连接服务器的EMQ (mqtt服务器),但是在QT里返回SocketRemoteHostClosedError错误码；通过抓包分析，客户端发送了client hello，但是服务端没有返回server hello，直接被服务端断开了。
CA证书信息打印如下：
SSL PrivateKey= QSslKey(PrivateKey, RSA, 2048)
SSL Certificate= QSslCertificate("1", "cf:92:41:43:f2:2b:21:df", "5Ltrx4+lQOYuU3xgmo9+kA==", (), (), QMap(), QDateTime(2018-07-03 09:32:51.000 UTC Qt::TimeSpec(UTC)), QDateTime(2023-07-02 09:32:51.000 UTC Qt::TimeSpec(UTC)))
SSL rootCA= (QSslCertificate("3", "90:df:de:17:8d:6d:f3:fa", "NNWCXsw6NZACk5nwTB5d4w==", (), (), QMap(), QDateTime(2018-07-03 09:32:50.000 UTC Qt::TimeSpec(UTC)), QDateTime(2023-07-02 09:32:50.000 UTC Qt::TimeSpec(UTC))))

emq日志打印如下：
2020-03-15 00:15:15.814 connection failed to establish: {ssl_error,
{tls_alert,
{certificate_unknown,
"TLS server: In state certify received CLIENT ALERT: Fatal - Certificate Unknown\n"}}}
2020-03-15 00:15:15.888 connection failed to establish: {ssl_error,
{tls_alert,
{certificate_unknown,
"TLS server: In state certify received CLIENT ALERT: Fatal - Certificate Unknown\n"}}}
2020-03-15 00:15:16.718 connection failed to establish: {ssl_error,
{tls_alert,
{certificate_unknown,
"TLS server: In state certify received CLIENT ALERT: Fatal - Certificate Unknown\n"}}}