WPF

public class UserCredentialsHeaderContent
{
    public string UserName { get; set; }
    public string Password { get; set; }

    public UserCredentialsHeaderContent(string userName, string password)
    {
        UserName = userName;
        Password = password;
    }

    public UserCredentialsHeaderContent()
    {

    }
}

public class UserCredentialsMessageHeader : MessageHeader
    {
        private const string HEADER_NAME = "UserToken";
        private const string HEADER_NAMESPACE = "NameSpace";

        public UserCredentialsHeaderContent UserCredentials { get; private set; }

        public override string Name
        {
            get { return HEADER_NAME; }
        }

        public override string Namespace
        {
            get { return HEADER_NAMESPACE; }
        }

        public UserCredentialsMessageHeader()
        {

        }

        public UserCredentialsMessageHeader(UserCredentialsHeaderContent userCredentials)
        {
            UserCredentials = userCredentials;
        }

        protected override void OnWriteHeaderContents(XmlDictionaryWriter writer, MessageVersion messageVersion)
        {
            XmlSerializer serializer = new XmlSerializer(typeof(UserCredentialsHeaderContent));
            StringWriter stringWriter = new StringWriter();
            serializer.Serialize(stringWriter, UserCredentials);
            stringWriter.Close();

            string text = stringWriter.ToString();
            writer.WriteElementString(HEADER_NAME, HEADER_NAMESPACE, text);
        }

        public static UserCredentialsHeaderContent ReadHeader(Message request)
        {
            int headerIndex = request.Headers.FindHeader(HEADER_NAME, HEADER_NAMESPACE);
            if (headerIndex != -1)
            {
                XmlNode[] contentNode = request.Headers.GetHeader<XmlNode[]>(headerIndex);
                string text = contentNode[0].InnerText;

                XmlSerializer deSerializer = new XmlSerializer(typeof(UserCredentialsHeaderContent));
                StringReader stringReader = new StringReader(text);
                UserCredentialsHeaderContent content = (UserCredentialsHeaderContent)  deSerializer.Deserialize(stringReader);
                stringReader.Close();

                return content;
            }
            else
            {
                return null;
            }
        }
    }

public class ClientMessageInspector :  IClientMessageInspector
    {

        #region IClientMessageInspectorImplementation
        public object BeforeSendRequest(ref Message request, IClientChannel channel)
        {

            UserCredentialsMessageHeader msgHeader = new UserCredentialsMessageHeader(
                new UserCredentialsHeaderContent("UserName", "Password"));
            request.Headers.Add(msgHeader);
            return null;
        }

        public void AfterReceiveReply(ref Message reply, object correlationState)
        {

        }
    }

public class TestService : ITestService
    {
        public string SendMessage(string message)
        {

            UserCredentialsHeaderContent content =
                OperationContext.Current.IncomingMessageHeaders.GetHeader<UserCredentialsHeaderContent>("UserToken", "NameSpace");
            return "Hello " + message;
        }
    }