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WCF Client Injection with Client Certificate from File Tutorial

This tutorial aims to teach you how to use the WCF Client Injection extension to Unity 1.2 (found in the DigitallyCreated.Utilities.Unity assembly) inject WCF clients that use a client certificate that was loaded from a file. It is assumed you are familiar with C#, WCF, Unity and the previous tutorial.

There are some cases where you can't use WCF's configuration XML (system.serviceModel) to specify a client certificate to use in a binding configuration. The XML binding configuration only lets you specify details about the certificate to be pulled from the local system certificate store. The use case I came across was on ASP.NET shared hosting where you can't install arbitrary certificates in the certificate store, so I needed to load the certificate from a file on disk instead.

Normally to load a certificate from a file on disk and use it in a binding configuration you'd need to write your binding configuration in C# or write the majority of it in XML, then modify it in C# to provide the file-loaded certificate. Obviously, with dependency injection, you have no (or little) control over how the WCF client constructed and configured.

In the last tutorial, the WCF Client Injection extension to Unity injected a WCF client for the IMyService interface. It did this by, behind the scenes, using a ChannelFactory<T> to create a WCF client with specified endpoint configuration. The ChannelFactory<T> needs to be told up front at construction time the binding configuration to use. The WCF Client Injection extension to Unity abstracts away the construction of a ChannelFactory<T> behind the IChannelFactoryFactory interface. The concrete class EndpointConfigurationChannelFactoryFactory is used by default to create ChannelFactory<T>s.

But in our case, where we want to customise the endpoint binding configuration with a file-loaded client certificate, the default IChannelFactoryFactory isn't cutting it. Thankfully, there is a way to choose a different IChannelFactoryFactory to use. DigitallyCreated.Utilities.Unity contains another IChannelFactoryFactory that will allow us to use a file-loaded client certificates: the ClientCertificateFromFileChannelFactoryFactory. (And in the same fashion, if you need to do something that isn't supported by any of the out of the box IChannelFactoryFactorys, you can create your own and use it).

So, to use the ClientCertificateFromFileChannelFactoryFactory, we need to customise the serviceInterface XML element we used in the last tutorial:

<serviceInterface type="MyServices.IMyService, MyServicesAssembly">
        cfgElementType="DigitallyCreated.Utilities.Unity.Configuration.ClientCertificateFromFileChannelFactoryFactoryConfElement, DigitallyCreated.Utilities.Unity"
        certPassword="" />

Note that our serviceInterface element now contains a customChannelFactoryFactory element. The cfgElementType attribute specifies the .NET class to use to deserialize the custom configuration element (in this case, for the ClientCertificateFromFileChannelFactoryFactory, its the hugely named ClientCertificateFromFileChannelFactoryFactoryConfElement). Notice the endpoint configuration's name has shifted from the serviceInterface element to the customChannelFactoryFactory. This is because using the endpointConfiguration attribute on the serviceInterface element is just shorthand for telling the extension to use the default EndpointConfigurationChannelFactoryFactory. The certificate's filename is specified in certFilename and the password to access it is specified in certPassword.

And that's it. That custom configuration element class will take care of wiring in the use of the ClientCertificateFromFileChannelFactoryFactory.

Last edited Mar 22, 2010 at 9:05 AM by dchambers, version 1


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