SF_14.4, SF_15.0, SF_15.1 - https://www.progress.com/documentation/sitefinity-cms/for-developers-secure-your-custom-servicestack-web-service

Startup.cs

using IdentityServer3.AccessTokenValidation;
using Owin;
using Telerik.Sitefinity.Authentication.Owin.OpenId;
using Telerik.Sitefinity.Owin;

namespace SitefinityWebApp.DeleteOrphanedUserProfiles
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            // Register default Sitefinity middlewares in the pipeline
            app.UseSitefinityMiddleware();

        }
    }
}