WCF custom headers in .NET CF

Hello

I created a WCF service, which has a single endpoint and uses BasicHttpBinding, so it can be accessed by mobile clients. The service(for now) does not use security. I want to create an authentication mechanisem with CustomHeader-s. The client(a windows mobile device) calls a register method and adds a custom header with user credentials to the message. The service validates supplied credentials and returns a GUID - again in the CustomHeader. The problem is that I dot't know how to access the header on the client side. I tried to get header in the

private TRESPONSE getResult(System.ServiceModel.Channels.Message reply, CFInvokeInfo info) { }

method, where I make a call to the following method.

public static string ReadHeader(Message request, XmlObjectSerializer serializer) { int headerIndex = request.Headers.FindHeader(HEADER_NAME, HEADER_NAMESPACE); if (headerIndex != -1) { XmlNode[] contentNode = request.Headers.GetHeader<XmlNode[]>(headerIndex, serializer); string text = contentNode[0].InnerText; XmlSerializer deSerializer = new XmlSerializer(typeof(string)); StringReader reader = new StringReader(text); string content = (string)deSerializer.Deserialize(reader); reader.Close(); return content; } else { return null; } }

The problem is in the following line

XmlNode[] contentNode = request.Headers.GetHeader<XmlNode[]>(headerIndex, serializer);

where I get an InvalidCastException.
Does anybody knows what am I doing wrong? Any ideas will be appreciated.