Bouncy castle generate self signed certificate with a key

First we generate an RSA key pair, then we add the certificate attributes and finally create a signature factory (instead of the deprecated way of using the private key directly).

public void GenerateCertificateWithKey(string subjectDn)
{
       RsaKeyPairGenerator rsaKeyGenerator = new ();
       KeyGenerationParameters keyGenerationParameters = new (new SecureRandom(), 2048);
       rsaKeyGenerator.Init (keyGenerationParameters);
       AsymmetricCipherKeyPair pair = rsaKeyGenerator.GenerateKeyPair();

       X509Name subjectName = new (subjectDn);

       X509V3CertificateGenerator certGenerator = new();
       certGenerator.SetSerialNumber(BigInteger.ValueOf(DateTime.Now.Ticks));
       certGenerator.SetIssuerDN(subjectName);
       certGenerator.SetNotBefore(DateTime.UtcNow);
       certGenerator.SetNotAfter(DateTime.UtcNow.AddYears(4));
       certGenerator.SetSubjectDN(subjectName);
       certGenerator.SetPublicKey(pair.Public);

       certGenerator.AddExtension(X509Extensions.BasicConstraints, true,
               new BasicConstraints(false));
       certGenerator.AddExtension(X509Extensions.KeyUsage, true, new KeyUsage(
               KeyUsage.NonRepudiation));

       ISignatureFactory signatureFactory = new Asn1SignatureFactory("SHA512WITHRSA", pair.Private, new SecureRandom());

       var cert = certGenerator.Generate(signatureFactory);
}