Qt OPC UA X509 Support

 // Copyright (C) 2019 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

 #include <QOpcUaKeyPair>
 #include <QOpcUaProvider>
 #include <QOpcUaX509CertificateSigningRequest>
 #include <QOpcUaX509ExtensionBasicConstraints>
 #include <QOpcUaX509ExtensionExtendedKeyUsage>
 #include <QOpcUaX509ExtensionKeyUsage>
 #include <QOpcUaX509ExtensionSubjectAlternativeName>
 #include <QFile>

 using namespace Qt::StringLiterals;

 int main(int argc, char **argv)
 {
     Q_UNUSED(argc);
     Q_UNUSED(argv);

     // Generate RSA Key
     QOpcUaKeyPair key;
     key.generateRsaKey(QOpcUaKeyPair::RsaKeyStrength::Bits2048);

     // Save private key to file
     QByteArray keyData = key.privateKeyToByteArray(QOpcUaKeyPair::Cipher::Unencrypted, QString());

     QFile keyFile(u"privateKey.pem"_s);
     keyFile.open(QFile::WriteOnly);
     keyFile.write(keyData);
     keyFile.close();

     // Create a certificate signing request
     QOpcUaX509CertificateSigningRequest csr;

     // Set the subject of the certificate
     QOpcUaX509DistinguishedName dn;
     dn.setEntry(QOpcUaX509DistinguishedName::Type::CommonName, u"QtOpcUaViewer"_s);
     dn.setEntry(QOpcUaX509DistinguishedName::Type::CountryName, u"DE"_s);
     dn.setEntry(QOpcUaX509DistinguishedName::Type::LocalityName, u"Berlin"_s);
     dn.setEntry(QOpcUaX509DistinguishedName::Type::StateOrProvinceName, u"Berlin"_s);
     dn.setEntry(QOpcUaX509DistinguishedName::Type::OrganizationName, u"The Qt Company"_s);
     csr.setSubject(dn);

     // The subject alternative name extension is needed for OPC UA
     QOpcUaX509ExtensionSubjectAlternativeName *san = new QOpcUaX509ExtensionSubjectAlternativeName;
     san->addEntry(QOpcUaX509ExtensionSubjectAlternativeName::Type::DNS, u"foo.com"_s);
     san->addEntry(QOpcUaX509ExtensionSubjectAlternativeName::Type::URI, u"urn:foo.com:The%20Qt%20Company:QtOpcUaViewer"_s);
     san->setCritical(true);
     csr.addExtension(san);

     // Set the certificate basic constraints
     QOpcUaX509ExtensionBasicConstraints *bc = new QOpcUaX509ExtensionBasicConstraints;
     bc->setCa(false);
     bc->setCritical(true);
     csr.addExtension(bc);

     // The required values for key usage and extended key usage are defined in OPC UA Part 6, 6.2.2, Table 43

     // Set the key usage constraints
     QOpcUaX509ExtensionKeyUsage *ku = new QOpcUaX509ExtensionKeyUsage;
     ku->setCritical(true);
     ku->setKeyUsage(QOpcUaX509ExtensionKeyUsage::KeyUsage::DigitalSignature);
     ku->setKeyUsage(QOpcUaX509ExtensionKeyUsage::KeyUsage::NonRepudiation);
     ku->setKeyUsage(QOpcUaX509ExtensionKeyUsage::KeyUsage::KeyEncipherment);
     ku->setKeyUsage(QOpcUaX509ExtensionKeyUsage::KeyUsage::DataEncipherment);
     csr.addExtension(ku);

     // Set the extended key usage constraints
     QOpcUaX509ExtensionExtendedKeyUsage *eku = new QOpcUaX509ExtensionExtendedKeyUsage;
     eku->setCritical(true);
     eku->setKeyUsage(QOpcUaX509ExtensionExtendedKeyUsage::KeyUsage::TlsWebClientAuthentication);
     csr.addExtension(eku);

     // Now there are two options:
     // 1. When you need to get your certificate signing request signed by a certificate authority
     //    you have to use the request data.
     // 2. When there is no certificate authority you have to self-sign the request.

     // Option 1
     QByteArray certificateSigningRequestData = csr.createRequest(key);

     // Option 2
     QByteArray selfSignedCertificateData = csr.createSelfSignedCertificate(key);

     return 0;
 }