ASP.NET Core 2.0 Preview 1: How to set up Cookie Authentication with custom login path

In ASP.NET Core 2.0 the .UseAuthentication() middleware has a breaking change that no longer allows the old syntax mentioned here to work.

The new version appears to deal with config in addAuthentication, but I can't find any details anywhere on how to change my old code that specified a custom login and logout url.

        services.AddAuthentication(o =>
        {
            // Where can I specify this?????
            var opt = new CookieAuthenticationOptions()
            {
                LoginPath = "/api/login",
                LogoutPath = "/api/logout",
            };

           o.DefaultSignInScheme = CookieAuthenticationDefaults.AuthenticationScheme;
           o.DefaultAuthenticateScheme = CookieAuthenticationDefaults.AuthenticationScheme;
        });

Any help would be appreciated...