ServiceStack MQ: how to populate data in RequestContext

I'm developing a JWT-based multi-tenancy system using ServiceStack. The JWT token contains shard information, and I use JwtAuthProvider to translate the JWT token to session object following instructions at http://docs.servicestack.net/jwt-authprovider.

Now, I want to use ServiceStack MQ for asynchronous processing. The MQ request needs to be aware of the shard information, so I populate the request context before executing it as follow

mqServer.RegisterHandler<EmployeeAssignedToProject>(m =>
            {
                var req = new BasicRequest { Verb = HttpMethods.Post };
                var sessionKey = SessionFeature.GetSessionKey(m.GetBody().SessionId);
                var session = HostContext.TryResolve<ICacheClient>().Get<Context>(sessionKey);
                req.Items[Keywords.Session] = session;
                var response = ExecuteMessage(m, req);
                return response;
            });

Here, Context is my custom session class. This technique is stemmed from the instruction at http://docs.servicestack.net/messaging#authenticated-requests-via-mq. Since I execute the message within the context of req, I reckon that I should then be able to resolve Context as follow

container.AddScoped<Context>(c =>
        {
            var webRequest = HostContext.TryGetCurrentRequest();
            if (webRequest != null)
            {
                return webRequest.SessionAs<Context>();
            } else
            {
                return HostContext.RequestContext.Items[Keywords.Session] as Context;                    
            }
        });

However, HostContext.RequestContext.Items is always empty. So the question is, how to populate HostContext.RequestContext.Items from within message handler registration code?

I've tried to dig a little bit into ServiceStack code and found that the ExecuteMessage(IMessage dto, IRequest req) in ServiceController doesn't seem to populate data in RequestContext. For my case, it is a bit too late to get session inside service instance, as a service instance depends on some DB connections whose shard info is kept in session.

The same Request Context instance can't be resolved from the IOC. The Request Context instance is created in the MQ's RegisterHandler<T>() where you can add custom data in the IRequest.Items property, e.g:

mqServer.RegisterHandler<EmployeeAssignedToProject>(m =>
{
    var req = new BasicRequest { Verb = HttpMethods.Post };
    req.Items[MyKey] = MyValue; //Inject custom per-request data
    //...
    var response = ExecuteMessage(m, req);
    return response;
});

This IRequest instance is available throughout the Request pipeline and from base.Request in your Services. It's not available from your IOC registrations so you will need to pass it in as an argument when calling your dependency, e.g:

public class MyServices : Service
{
    public IDependency MyDep { get; set; }

    public object Any(MyRequest request) => MyDep.Method(base.Request, request.Id);
}