Custom Provider for Windows Authentication

Hello,

I would like to know how to develop a custom provider for Windows Authentication. I've an ASP.NET web application served with IIS 8.5 that authenticates using Windows Authentication. The problem is that I also need to authenticate users asking a custom web service (in addition to the local users and active directory)

How can I achieve this? Forms authentication is not a solution because I need to authenticate in otherapps (Reporting Services and Analysis Services) with the same credentials from the ASP.NET app and both application have the authentication and authorization configured with Windows Authentication.

Thanks in advance,