System.Net.Http.CurlHandler.SslProvider.SslCtxCallback C# (CSharp) Method

            private static CURLcode SslCtxCallback(IntPtr curl, IntPtr sslCtx, IntPtr userPointer)
            {
                EasyRequest easy;
                if (!TryGetEasyRequest(curl, out easy))
                {
                    return CURLcode.CURLE_ABORTED_BY_CALLBACK;
                }

                // Configure the SSL protocols allowed.
                SslProtocols protocols = easy._handler.SslProtocols;
                if (protocols == SslProtocols.None)
                {
                    // If None is selected, let OpenSSL use its defaults, but with SSL2/3 explicitly disabled.
                    // Since the shim/OpenSSL work on a disabling system, where any protocols for which bits aren't
                    // set are disabled, we set all of the bits other than those we want disabled.
#pragma warning disable 0618 // the enum values are obsolete
                    protocols = ~(SslProtocols.Ssl2 | SslProtocols.Ssl3);
#pragma warning restore 0618
                }
                Interop.Ssl.SetProtocolOptions(sslCtx, protocols);

                // Configure the SSL server certificate verification callback.
                Interop.Ssl.SslCtxSetCertVerifyCallback(sslCtx, s_sslVerifyCallback, curl);

                // If a client certificate provider was provided, also configure the client certificate callback.
                if (userPointer != IntPtr.Zero)
                {
                    try
                    {
                        // Provider is passed in via a GCHandle.  Get the provider, which contains
                        // the client certificate callback delegate.
                        GCHandle handle = GCHandle.FromIntPtr(userPointer);
                        ClientCertificateProvider provider = (ClientCertificateProvider)handle.Target;
                        if (provider == null)
                        {
                            Debug.Fail($"Expected non-null provider in {nameof(SslCtxCallback)}");
                            return CURLcode.CURLE_ABORTED_BY_CALLBACK;
                        }

                        // Register the callback.
                        Interop.Ssl.SslCtxSetClientCertCallback(sslCtx, provider._callback);
                        EventSourceTrace("Registered client certificate callback.", easy: easy);
                    }
                    catch (Exception e)
                    {
                        Debug.Fail($"Exception in {nameof(SslCtxCallback)}", e.ToString());
                        return CURLcode.CURLE_ABORTED_BY_CALLBACK;
                    }
                }

                return CURLcode.CURLE_OK;
            }