Why does it need to be stand alone?
FYI, in svn trunk I already have a WCF AuthenticationService at Web/Services/AuthenticationService.svc.
I also have a WCF role service at Web/Services/RoleService.svc.
I am using both currently from Silverlight.
Its possible to create a separate WCF project and reference mojoPortal.Web project to be able to use these providers.
Internally these providers have dependencies on other mojoportal objects and HttpContext is required to get SiteSettings object from the cache. I see no reason to avoid dependency on httpcontext in a web application or WCF application.