How to tell if SPUser is Active Directory account

Question

I'm working on a project where the client wants to restrict some content to only Active Directory users . Is there any way to identify that a SPUser is an AD user short of parsing the username string for the domain (or something along those lines). Something like SPUser.IsADUser would be awesome.

Edit This seems to work, but I'm not sure if this is reliable enough? For this use case, identifying that a user is a windows user is enough (there are no local system accounts)

SPUser user = SPContext.Current.Web.CurrentUser;
string userName = user.LoginName.Substring(user.LoginName.IndexOf('|') + 1);
SPPrincipalInfo info = SPUtility.ResolveWindowsPrincipal(SPContext.Current.Site.WebApplication, userName, SPPrincipalType.User, false);
if(info != null){
    //THIS IS A WINDOWS ACCOUNT
}

Answer 1

In my experience it is much better to use audiences for this purpose. You then can easily trim any web part using "Audience" property. You can read about audiences here. Of course it will only work if you have user profile synchronization configured.