访问Unity WebApi2 C#?中的请求头?

我想创造一个 RegisterType 基于Unity中的请求头,C#。

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 );
}));

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

如何在Unity5.2.0中访问请求头。