I’m creating a CSR file to request a certificate from AD CA, and I need to obtain both the public and private keys for use in digital signatures. However, in response from AD CA, I only receive the public key, and the private key is not exportable. How can I set the Exportable flag to true in the request, or is there something else I need to do to obtain an exportable private key in .pfx format?

            // Constructing osVersion extension
            DerObjectIdentifier osVersionOID = new DerObjectIdentifier("1.3.6.1.4.1.311.13.2.3");
            ...

            // Constructing extensionRequest extension
            DerObjectIdentifier extensionRequestOID = new DerObjectIdentifier("1.2.840.113549.1.9.14");
            DerObjectIdentifier subjectKeyIdentifierOID = new DerObjectIdentifier("2.5.29.14");
            ...

            // Constructing requestClientInfo extension
            DerObjectIdentifier requestClientInfoOID = new DerObjectIdentifier("1.3.6.1.4.1.311.21.20");
            ...

            DerObjectIdentifier enrolmentCSPOID = new DerObjectIdentifier("1.3.6.1.4.1.311.13.2.2");
            ...

            // Constructing the CSR
            Asn1EncodableVector csrAttributes = new Asn1EncodableVector();
            csrAttributes.Add(osVersionExtension);
            csrAttributes.Add(extensionRequestExtension);
            csrAttributes.Add(requestClientInfoExtension);
            csrAttributes.Add(enrolmentCSPExtension);
          
            // Generate RSA key pair
            RsaKeyPairGenerator generator = new RsaKeyPairGenerator();
            generator.Init(new Org.BouncyCastle.Crypto.KeyGenerationParameters(new SecureRandom(), 2048));
    
            AsymmetricCipherKeyPair keyPair = generator.GenerateKeyPair();
            
            // Make private key exportable
            CspParameters cspParams = new CspParameters()
            {
                KeyContainerName = Guid.NewGuid().ToString(),
                KeyNumber = (int)KeyNumber.Exchange,
                Flags = CspProviderFlags.UseMachineKeyStore  //CspProviderFlags.NoPrompt | CspProviderFlags.UseMachineKeyStore | CspProviderFlags.UseExistingKey
            };

            var privateKey = (RsaPrivateCrtKeyParameters)keyPair.Private;
           
            RSACryptoServiceProvider rsaProvider = new RSACryptoServiceProvider(cspParams);
       //     rsaProvider.ExportParameters(true);
            var parameters = new RSAParameters
            {
                Modulus = privateKey.Modulus.ToByteArrayUnsigned(),
                P = privateKey.P.ToByteArrayUnsigned(),
                Q = privateKey.Q.ToByteArrayUnsigned(),
                DP = privateKey.DP.ToByteArrayUnsigned(),
                DQ = privateKey.DQ.ToByteArrayUnsigned(),
                InverseQ = privateKey.QInv.ToByteArrayUnsigned(),
                D = privateKey.Exponent.ToByteArrayUnsigned(),
                Exponent = privateKey.PublicExponent.ToByteArrayUnsigned()

            };
            
            rsaProvider.ImportParameters(parameters);
            rsaProvider.PersistKeyInCsp = true;
            
            Console.WriteLine("CSR Exportable:" + rsaProvider.CspKeyContainerInfo.Exportable);
            Console.WriteLine("CSR PublicOnly:" + rsaProvider.PublicOnly);
  
            AsymmetricCipherKeyPair bcKeyPair = DotNetUtilities.GetRsaKeyPair(rsaProvider);
                 
            // Create CSR
            Pkcs10CertificationRequest csr = new Pkcs10CertificationRequest("SHA256WITHRSA",
               new X509Name("CN=AD User Name"), // 
                bcKeyPair.Public, //keyPair.Public,  
                new DerSet(csrAttributes),
                bcKeyPair.Private);

            // Output CSR
            Console.WriteLine("CSR in PEM format:");
            Console.WriteLine(PemEncodeCsr(csr));
            Console.ReadLine();
        }
        static string PemEncodeCsr(Pkcs10CertificationRequest csr)
        {
            return "-----BEGIN CERTIFICATE REQUEST-----n" +
                   Convert.ToBase64String(csr.GetEncoded(), Base64FormattingOptions.InsertLineBreaks) +
                   "n-----END CERTIFICATE REQUEST-----";
        }

I tried to change the flags in CspParameters, but it doesn’t affect the result.