System.Security.Cryptography.X509Certificates.X509Certificate2.CreateCustomExtensionIfAny C# (CSharp) Method

        private static X509Extension CreateCustomExtensionIfAny(Oid oid)
        {
            string oidValue = oid.Value;
            switch (oidValue)
            {
                case Oids.BasicConstraints:
                    return X509Pal.Instance.SupportsLegacyBasicConstraintsExtension ?
                        new X509BasicConstraintsExtension() :
                        null;

                case Oids.BasicConstraints2:
                    return new X509BasicConstraintsExtension();

                case Oids.KeyUsage:
                    return new X509KeyUsageExtension();

                case Oids.EnhancedKeyUsage:
                    return new X509EnhancedKeyUsageExtension();

                case Oids.SubjectKeyIdentifier:
                    return new X509SubjectKeyIdentifierExtension();

                default:
                    return null;
            }
        }

        private static unsafe CertificateRequest LoadSigningRequest(
            ReadOnlySpan <byte> pkcs10,
            bool permitTrailingData,
            HashAlgorithmName signerHashAlgorithm,
            out int bytesConsumed,
            CertificateRequestLoadOptions options,
            RSASignaturePadding?signerSignaturePadding)
        {
            ArgumentException.ThrowIfNullOrEmpty(signerHashAlgorithm.Name, nameof(signerHashAlgorithm));

            if ((options & ~AllOptions) != 0)
            {
                throw new ArgumentOutOfRangeException(nameof(options), options, SR.Argument_InvalidFlag);
            }

            bool skipSignatureValidation =
                (options & CertificateRequestLoadOptions.SkipSignatureValidation) != 0;

            bool unsafeLoadCertificateExtensions =
                (options & CertificateRequestLoadOptions.UnsafeLoadCertificateExtensions) != 0;

            try
            {
                AsnValueReader outer         = new AsnValueReader(pkcs10, AsnEncodingRules.DER);
                int            encodedLength = outer.PeekEncodedValue().Length;

                AsnValueReader     pkcs10Asn = outer.ReadSequence();
                CertificateRequest req;

                if (!permitTrailingData)
                {
                    outer.ThrowIfNotEmpty();
                }

                fixed(byte *p10ptr = pkcs10)
                {
                    using (PointerMemoryManager <byte> manager = new PointerMemoryManager <byte>(p10ptr, encodedLength))
                    {
                        ReadOnlyMemory <byte>       rebind             = manager.Memory;
                        ReadOnlySpan <byte>         encodedRequestInfo = pkcs10Asn.PeekEncodedValue();
                        CertificationRequestInfoAsn requestInfo;
                        AlgorithmIdentifierAsn      algorithmIdentifier;
                        ReadOnlySpan <byte>         signature;
                        int signatureUnusedBitCount;

                        CertificationRequestInfoAsn.Decode(ref pkcs10Asn, rebind, out requestInfo);
                        AlgorithmIdentifierAsn.Decode(ref pkcs10Asn, rebind, out algorithmIdentifier);

                        if (!pkcs10Asn.TryReadPrimitiveBitString(out signatureUnusedBitCount, out signature))
                        {
                            throw new CryptographicException(SR.Cryptography_Der_Invalid_Encoding);
                        }

                        pkcs10Asn.ThrowIfNotEmpty();

                        if (requestInfo.Version < 0)
                        {
                            throw new CryptographicException(SR.Cryptography_Der_Invalid_Encoding);
                        }

                        // They haven't bumped from v0 to v1 as of 2022.
                        const int MaxSupportedVersion = 0;

                        if (requestInfo.Version != MaxSupportedVersion)
                        {
                            throw new CryptographicException(
                                      SR.Format(
                                          SR.Cryptography_CertReq_Load_VersionTooNew,
                                          requestInfo.Version,
                                          MaxSupportedVersion));
                        }

                        PublicKey publicKey = PublicKey.DecodeSubjectPublicKeyInfo(ref requestInfo.SubjectPublicKeyInfo);

                        if (!skipSignatureValidation)
                        {
                            // None of the supported signature algorithms support signatures that are not full bytes.
                            // So, shortcut the verification on the bit length
                            if (signatureUnusedBitCount != 0 ||
                                !VerifyX509Signature(encodedRequestInfo, signature, publicKey, algorithmIdentifier))
                            {
                                throw new CryptographicException(SR.Cryptography_CertReq_SignatureVerificationFailed);
                            }
                        }

                        X500DistinguishedName subject = new X500DistinguishedName(requestInfo.Subject.Span);

                        req = new CertificateRequest(
                            subject,
                            publicKey,
                            signerHashAlgorithm,
                            signerSignaturePadding);

                        if (requestInfo.Attributes is not null)
                        {
                            bool foundCertExt = false;

                            foreach (AttributeAsn attr in requestInfo.Attributes)
                            {
                                if (attr.AttrType == Oids.Pkcs9ExtensionRequest)
                                {
                                    if (foundCertExt)
                                    {
                                        throw new CryptographicException(
                                                  SR.Cryptography_CertReq_Load_DuplicateExtensionRequests);
                                    }

                                    foundCertExt = true;

                                    if (attr.AttrValues.Length != 1)
                                    {
                                        throw new CryptographicException(
                                                  SR.Cryptography_CertReq_Load_DuplicateExtensionRequests);
                                    }

                                    AsnValueReader extsReader = new AsnValueReader(
                                        attr.AttrValues[0].Span,
                                        AsnEncodingRules.DER);

                                    AsnValueReader exts = extsReader.ReadSequence();
                                    extsReader.ThrowIfNotEmpty();

                                    // Minimum length is 1, so do..while
                                    do
                                    {
                                        X509ExtensionAsn.Decode(ref exts, rebind, out X509ExtensionAsn extAsn);

                                        if (unsafeLoadCertificateExtensions)
                                        {
                                            X509Extension ext = new X509Extension(
                                                extAsn.ExtnId,
                                                extAsn.ExtnValue.Span,
                                                extAsn.Critical);

                                            X509Extension?rich =
                                                X509Certificate2.CreateCustomExtensionIfAny(extAsn.ExtnId);

                                            if (rich is not null)
                                            {
                                                rich.CopyFrom(ext);
                                                req.CertificateExtensions.Add(rich);
                                            }
                                            else
                                            {
                                                req.CertificateExtensions.Add(ext);
                                            }
                                        }
                                    } while (exts.HasData);
                                }
                                else
                                {
                                    if (attr.AttrValues.Length == 0)
                                    {
                                        throw new CryptographicException(SR.Cryptography_Der_Invalid_Encoding);
                                    }

                                    foreach (ReadOnlyMemory <byte> val in attr.AttrValues)
                                    {
                                        req.OtherRequestAttributes.Add(
                                            new AsnEncodedData(attr.AttrType, val.Span));
                                    }
                                }
                            }
                        }
                    }
                }

                bytesConsumed = encodedLength;
                return(req);
            }
            catch (AsnContentException e)
            {
                throw new CryptographicException(SR.Cryptography_Der_Invalid_Encoding, e);
            }
        }