asp.net Web应用程序-检查用户是否存在于Active Directory组中

public List<string> GetGroupNames(string userName)
{
    var pc = new PrincipalContext(ContextType.Domain);
    var src = UserPrincipal.FindByIdentity(pc, userName).GetGroups(pc);
    var result = new List<string>();
    src.ToList().ForEach(sr => result.Add(sr.SamAccountName));
    return result;
}

    if (HttpContext.Current.User.IsInRole(\"RoleName\"))
    {
        return true;
    }
    else
    {
        return false;
    }