Adding Http Header in an existing WCF SOAP Service is not working

If you are trying to add an HTTP request header to the client request, you can follow the procedure below.

Create a client message inspector. For example:

public class CustomInspector : IClientMessageInspector
{
    public void AfterReceiveReply(ref Message reply, object correlationState)
    {
    }

    public object BeforeSendRequest(ref Message request, IClientChannel channel)
    {
        HttpRequestMessageProperty reqProps = request.Properties[HttpRequestMessageProperty.Name] as HttpRequestMessageProperty;
        if(reqProps == null)
        {
            reqProps = new HttpRequestMessageProperty();
        }

        reqProps.Headers.Add("Custom-Header", "abcd");
        request.Properties[HttpRequestMessageProperty.Name] = reqProps;

        return null;
    }
}

Create an endpoint behavior to load this inspector:

public class CustomBehavior : IEndpointBehavior
{
    public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)
    {
    }

    public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
    {
        clientRuntime.ClientMessageInspectors.Add(new CustomInspector());
    }

    public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
    {
    }

    public void Validate(ServiceEndpoint endpoint)
    {
    }
}

Finally add this behavior to the endpoint.

class Program
{
    static void Main(string[] args)
    {
        ChannelFactory<ICalculator> factory = new ChannelFactory<ICalculator>("BasicHttpsBinding_ICalculator");
        factory.Endpoint.EndpointBehaviors.Add(new CustomBehavior());
        var client = factory.CreateChannel();

        var number = client.Add(1, 2);

        Console.WriteLine(number.ToString());
    }
}

The above example works on my side. I could see the request header with Fiddler.

SOAP Header

To add a SOAP header, use the following code client-side:

using (OperationContextScope scope = new OperationContextScope((IContextChannel)channel))
{
    MessageHeader<string> header = new MessageHeader<string>("MyHttpHeaderValue");
    var untyped = header.GetUntypedHeader("User-Auth", ns);
    OperationContext.Current.OutgoingMessageHeaders.Add(untyped);

    // now make the WCF call within this using block
}

And then, server-side, grab it using:

MessageHeaders headers = OperationContext.Current.IncomingMessageHeaders;
string identity = headers.GetHeader<string>("User-Auth", ns);

NB. ns is The namespace URI of the header XML element.

HTTP Header

To add an Http header:

// Add a HTTP Header to an outgoing request 
HttpRequestMessageProperty requestMessage = new HttpRequestMessageProperty();
requestMessage.Headers["MyHttpHeader"] = "MyHttpHeaderValue";
OperationContext.Current.OutgoingMessageProperties[HttpRequestMessageProperty.Name] = requestMessage;

And to grab it server-side

IncomingWebRequestContext request = WebOperationContext.Current.IncomingRequest; 
WebHeaderCollection headers = request.Headers; 
Console.WriteLine(request.Method + " " + request.UriTemplateMatch.RequestUri.AbsolutePath); 

foreach (string headerName in headers.AllKeys)
{ 
    Console.WriteLine(headerName + ": " + headers[headerName]); 
}