访问Unity WebApi2 C＃中的请求标头？

Question

我想基于Unity C＃中的请求标头创建一个RegisterType。

var container = new UnityContainer();
container.RegisterType<OrganizationServiceProxy>(new InjectionFactory(unityContainer =>
{
    var request = HttpContext.Current.Request; //Exception 'Request is not available in this context
    const string errorMessage = "Please add `CrmType` key to header to specify CRM type";
    var crmTypeString = request.Headers["CrmType"];
    .
    .
    .
    return new SOmeObject(crmTypeString );
}));

但是发生了以下异常：
Request is not available in this context

如何通过Web访问Unity 5.2.0中的请求标头。