Is there such a thing as a SOAP proxy server or am I going to have to roll my own?

Question

Disclaimer: I've tried Googling for something that will do what I want, but no luck there. I'm hoping someone here might be able to lend a hand.

Background

I have a .NET class library that accesses a secure web service with the WSE 2.0 library. The web service provides a front-end to a central database (it's actually part of a data-sharing network spanning multiple customers) and the class library provides a simple wrapper around the web service calls to make it accessible from a legacy VB6 application. The legacy application uses the class library to retrieve and publish information to the web service. Currently, the application and class library DLL are both installed client-side on multiple workstations.

The Problem

The catch is that the web service we are accessing uses HTTPS and a valid X509 client certificate needs to be presented to the web service in order to access it. Since all of our components live on the client machine, this has led to deployment problems. For example, we have to download and install per-user certificates on each client machine, one for each user who might need to access the web service through our application. What's more, the web server itself must be accessed through a VPN (OpenVPN in particular), which means a VPN client has to be installed and configured on every client machine. It is a major pain (some of our customers have dozens of workstations).

The Proposed Solution

The proposed solution is to move all of this logic to a central server on the customer site. In this scenario, our legacy application would communicate with a local server, which will then go off and forward requests to the real web service. In addition, all of the X509 certificates would be installed on the server, instead of on each individual client computer, as part of the effort to simplify and centralize deployment.

So far, we've come up with three options:

• Find a ready-made SOAP proxy server which can take incoming HTTP-based SOAP requests, modify the Host header and routing-related parts of the SOAP message (so they are pointing to the real web server), open an SSL connection to the real web server, present the correct client certificate to the server (based on a username-to-certificate mapping), forward the modified request, read the response, convert it back to plaintext, and send it back to the client.
• Write a proxy server by hand that does everything I just mentioned.
• Think of completely different and hopefully better way to solve this problem.

Rationale

The rationale for trying to find and/or write a SOAP proxy server is that our existing .NET wrapper library wouldn't have to be modified at all. We would simply point it at the proxy server instead of the real web service endpoint, using a plain HTTP connection instead of HTTPS. The proxy server will handle the request, modify it to so that the real web service will accept it (i.e. things like changing the SOAPAction header so that it is correct), handle the SSL/certificate handshake, and send the raw response data back to the client.

However, this sounds like an awful hack to me me at best. So, what our my options here?

• Do I bite the bullet and write my own HTTP/SSL/SOAP/X509 aware proxy server to do all this?
• Or...is there a ready-made solution with an extensible enough API that I can easily make it do what I want
• Or...should I take a completely different approach?

The key issues we are trying to solve are (a) centralizing where certificates are stored to simplify installation and management of certificates and (b) setting things up so that the VPN connection to the web server only occurs from a single machine, instead of needing every client to have VPN client software installed.

Note we do not control the web server that is hosting the web service.

EDIT: To clarify, I have already implemented a (rather crappy) proxy server in C# that does meet the requirements, but something feels fundamentally wrong to me about this whole approach to the problem. So, ultimately, I am looking either for reassurance that I am on the right track, or helpful advice telling me I'm going about this the completely wrong way, and any tips for doing it a better way (if there is one, which I suspect there is).

Answer 1

There is a service virtualization tool from Microsoft available on Codeplex called the Managed Service Engine which is intended to decouple the client from the web service implementation. It might fill the bill or give you a running start. I haven't really investigated it thoroughly, just skimmed an article in MSDN and your description reminded me of it.

• http://www.codeplex.com/servicesengine
• http://msdn.microsoft.com/en-us/magazine/dd727511.aspx

Answer 2

I believe an ESB (Enterprise Service Bus) could be a viable, robust solution to your problem. There is an open source ESB called Mule, which I've never used. I did mess around with ALSB (AquaLogic Service Bus) a while back, but it would be expensive for what you are describing. Anyway, the thing that you would want to look at in particular is the routing. I'm not sure it would be a simple plug 'n play, but it is indeed another option.

Answer 3

Your security model doesn't make sense to me. What is the purpose of using HTTPS? Usually it is to authenticate the service to the clients. In that case, why does the server need to keep the clients' certificates? It is the clients who should be keeping the server's X509 Certificate.

Why do you need to go through VPN? If you need to authenticate clients, there are better ways to do that. You can either enable mutual authentication in SSL, or use XML-Security and possibly WS-Security to secure the service at the SOAP level. Even if you do use SSL to authenticate clients, you still shouldn't keep all the client certificates on the server, but rather use PKI and verify the client certificates to a trusted root.

Finally, specifically for your proposed proxy-based solution, I don't see why you need anything SOAP-specific. Don't you just need a web server that can forward any HTTP request to a remote HTTPS server? I don't know how to do this offhand, but I'd be investigating the likes of Apache and IIS...

Answer 4

Apache Camel would fit the bill perfectly. Camel is a lightweight framework for doing exactly this kind of application integration. I've used it to do some similar http proxying in the past.

Camel uses a very expressive DSL for defining routes between endpoint. In your case you want to stand up a server that is visible to all the client machines at your customer site and whatever requests it receives you want to route 'from' this endpoint 'to' your secure endpoint via https.

You'll need to create a simple class that defines the route. It should extend RouteBuilder and override the configure method

public class WebServiceProxy extends RouteBuilder
{
    public void configure()
    {
       from("jetty:http://0.0.0.0:8080/myServicePath")
                  .to("https://mysecureserver/myServicePath");
    }
}

Add this to a Camel context and you'll be good to go.

CamelContext context = new DefaultCamelContext();
context.addRoute(new WebServiceProxy());
context.start();

This route will create a webserver using jetty bound to 8080 on all local interfaces. Any reuqests sent to /myServicePath will get routed directly to your webservice defined by the uri "https://mysecureserver/myServicePath". You define the endpoints using simple uris and the dsl and camel takes care of the heavy lifting.

You may need to configure a keystore with your certs in in and make it available to the http component. Post again if you've trouble here ;)

I'd read the camel docs for the http component for more details, check the unit tests for the project too as they are chock full of examples and best practices.

HTH.

FYI: To have the http component use your keystore, you'll need to set the following properties

System.setProperty("javax.net.ssl.trustStore", "path/to/keystore");
System.setProperty("javax.net.ssl.trustStorePassword", "keystore-password");

Answer 5

You can also do this with Microsoft ISA Server, a commercial Proxy/Cache server. It will do many of the things you need out of the box. For anything that is not possible out of the box, you can write an extension to the server to get it done.

ISA Server is not free.

ISA is now being renamed to "Microsoft Forefront Threat Management Gateway".

It is much more than a web proxy server, though - it has support for many protocols and lots of features. Maybe more than you need.

Answer 6

You should look into WCF, which supports the WS-Addressing protocol. I believe I've seen articles (in MSDN, I think) on writing routers using WCF.

You should also get rid of WSE 2.0 as soon as possible. It's very badly obsolete (having been replaced by WSE 3.0, which is also obsolete). All of its functions have been superceded by WCF.