WCF - Injecting into a Custom UserNamePasswordValidator with MEF - wcf

Question

I have a WCF Service which is using DI via MEF. That part is working fine.
I also have a Custom UserNamePasswordValidator which works as long as I use a parameterless constructor and 'new' everything up. However I would like to introduce MEF into that as well.
The service is hosted in IIS so I have to intercept it somewhat to get MEF to work as it is.
I've provided cross sections of my code below and any help would be appreciated!
Here is my web.config: -
<behavior name="StandardServiceBehaviour">
<serviceDebug includeExceptionDetailInFaults="true" />
<serviceCredentials>
<userNameAuthentication userNamePasswordValidationMode="Custom"
customUserNamePasswordValidatorType=
"WebService.Validators.CustomUserNamePasswordValidator, WebService" />
</serviceCredentials>
<serviceMetadata httpGetEnabled="true" httpsGetEnabled="true" />
<dataContractSerializer maxItemsInObjectGraph="67108864" />
</behavior>
My custom validator is as follows: -
[Export(typeof(ICustomUserNamePasswordValidator))]
[PartCreationPolicy(CreationPolicy.Shared)]
public class CustomUserNamePasswordValidator : UserNamePasswordValidator, ICustomUserNamePasswordValidator
{
[ImportingConstructor]
public CustomUserNamePasswordValidator([NotNull] IConnectionProvider connectionProvider)
{
}
.....
}
I'm using a custom attribute on my Web Service called WebServiceExport, which subclasses the MEF Export attribute and includes an InstanceProvider: -
[WebServiceExport(typeof(IGeneralService))]
public class GeneralService : IGeneralService
{
....
}
Here is the Export Attribute: -
public class WebServiceExportAttribute : ExportAttribute, IContractBehavior, IContractBehaviorAttribute
{
public void ApplyDispatchBehavior(ContractDescription description, ServiceEndpoint endpoint, DispatchRuntime dispatch)
{
var contractType = description.ContractType;
dispatch.InstanceProvider = new MefInstanceProvider(contractType);
}
....
}
And finally here is the Instance Provider: -
public class MefInstanceProvider : IInstanceProvider
{
public MefInstanceProvider(Type serviceContract)
{
_serviceContract = serviceContract;
}
public object GetInstance(InstanceContext instanceContext, Message message)
{
BuildInstance(); //compose MEF parts
}
....
}