c# check if the user member of a group?

Question

I have a code that I use to check if the user is member of the AD, worked perfectly,

now I want to add the possibility to check if the user also a member of a group!

what do I need to modify to achieve that, I did some work, but it fails!

so here is my code:

        //Authenticate a User Against the Directory
        private bool Authenticate(string userName,string password, string domain)
        {

            if (userName == "" || password == "")
            {
                return false;
            }

            bool authentic = false;
            try
            {
                DirectoryEntry entry = new DirectoryEntry("LDAP://" + domain,userName, password);
                object nativeObject = entry.NativeObject;
                authentic = true;
            }
            catch (DirectoryServicesCOMException) { }
            return authentic;
        }

I want to make it like this:

private bool Authenticate(string userName,string password, string domain, string group)

Answer 1

This is not available on Windows XP or earlier.

Anyway, in order to check for group membership, you can use this code:

bool IsInGroup(string user, string group)
{
    using (var identity = new WindowsIdentity(user))
    {
        var principal = new WindowsPrincipal(identity);
        return principal.IsInRole(group);
    }
}

Answer 2

In ASP.Net you will use Page.User.IsInRole("RoleName") or in Windows you can use System.Threading.Thread.CurrentPrincipal.IsInRole("RoleName")