wcf: SecurityBindingElement.CreateUserNameOverTransportBindingElement() not supported.

possibly related to #9 but I wasn’t sure so I’m opening this because I wasn’t sure what the roadmap was.

I get this error when trying to use the SecurityBindingElement.CreateUserNameOverTransportBindingElement(); binding element as part of a CustomBinding

(running on OSX with .NET core RC2)

Here is my code

    public class AcmeServiceChannelFactory : ChannelFactory<AcmeService>
    {
        public AcmeServiceChannelFactory()
            : base(CreateDefaultBinding(), new EndpointAddress("https://acme.com/service.asmx"))
        {
            Credentials.UserName.UserName = "username";
            Credentials.UserName.Password = "password";
        }

        internal static Binding CreateDefaultBinding()
        {
            var binding = new CustomBinding();
            var securityBinding = SecurityBindingElement.CreateUserNameOverTransportBindingElement();
            securityBinding.IncludeTimestamp = false;
            securityBinding.SecurityHeaderLayout = SecurityHeaderLayout.Lax;
            binding.Elements.Add(securityBinding);
            var textbinding = new TextMessageEncodingBindingElement
            {
                MessageVersion = MessageVersion.Soap11,
                ReaderQuotas = new XmlDictionaryReaderQuotas
                {
                    MaxArrayLength = int.MaxValue,
                    MaxDepth = 64,
                    MaxStringContentLength = int.MaxValue
                }
            };

            binding.Elements.Add(textbinding);

            var httpsBinding = new HttpsTransportBindingElement
            {
                MaxReceivedMessageSize = int.MaxValue,
                MaxBufferSize = int.MaxValue
            };

            binding.Elements.Add(httpsBinding);
            binding.OpenTimeout =
            binding.ReceiveTimeout =
            binding.SendTimeout = TimeSpan.FromMinutes(5);
            return binding;
        }
    }

error:

System.PlatformNotSupportedException: TransportSecurityBindingElement.BuildChannelFactoryCore is not supported.
   at System.ServiceModel.Channels.TransportSecurityBindingElement.BuildChannelFactoryCore[TChannel](BindingContext context)
   at System.ServiceModel.Channels.Binding.BuildChannelFactory[TChannel](BindingParameterCollection parameters)
   at System.ServiceModel.Channels.ServiceChannelFactory.BuildChannelFactory(ServiceEndpoint serviceEndpoint, Boolean useActiveAutoClose)
   at System.ServiceModel.ChannelFactory.OnOpening()
   at System.ServiceModel.Channels.CommunicationObject.<System-ServiceModel-IAsyncCommunicationObject-OpenAsync>d__71.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.ServiceModel.Channels.CommunicationObject.<OpenAsyncInternal>d__70.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.ServiceModel.ChannelFactory.EnsureOpened()
   at System.ServiceModel.ChannelFactory`1.CreateChannel(EndpointAddress address, Uri via)