Adding SAN/other extensions to CSRs in c# BouncyCastle

I'm generating a CSR programmatically in Xamarin Android as follows

var subject = new X509Name(subjectName);
              
                // Generate the key Value Pair, which in our case is a public Key
                var random = new SecureRandom();
                const int strength = 2048;
                var keyGenerationParameters = new KeyGenerationParameters(random, strength);

                var keyPairGenerator = new RsaKeyPairGenerator();
                keyPairGenerator.Init(keyGenerationParameters);
                AsymmetricCipherKeyPair subjectKeyPair = keyPairGenerator.GenerateKeyPair();
    
                Pkcs10CertificationRequest csr = new Pkcs10CertificationRequest("SHA256WITHRSA", subject, subjectKeyPair.Public, null, subjectKeyPair.Private);

which works fine, but I can't find how to add an extension. There are multiple guides for java that use Pkcs10CertificationRequestFactory, which doesn't exist in the c# version. I assume this was changed to make it more .net style and less java, but I can't figure out where that functionality went. I can generate the X509Extension like

X509ExtensionsGenerator extensionsGenerator = new X509ExtensionsGenerator();

                Asn1EncodableVector vec = new Asn1EncodableVector();
                Asn1EncodableVector v = new Asn1EncodableVector();
                v.Add(new DerObjectIdentifier("1.3.6.1.4.1.311.20.2.3"));
                v.Add(new DerTaggedObject(true, 0, new DerUtf8String("devuser@dvam.local"))
                );
                
                Asn1Object gn = new DerTaggedObject(false, 0, new DerSequence(v));
                vec.Add(gn);
              
                extensionsGenerator.AddExtension(X509Extensions.SubjectAlternativeName, true, new
                DerSequence(vec));
                var ext = extensionsGenerator.Generate();

but this is where in java you would invoke the factory. The Pkcs10CertificationRequest constructor takes in a Asn1Set attributes, which I assume would be where you'd pass it, but Asn1Set.GetInstance doesn't work on any of the above objects.