Script or Code to import from AD to Sharepoint Group All users

Question

I'm looking for a script or code to make Sharepoint know 'bout users from active directory.. I have 3 domains and People Picker sees people but cannot resolve that (suggest only).. I read in many place that to EnsureUser, Sharepoint must know 'bout them so that if I manually add user to sharepoint it works..

How can I do to add entire Active Directory users to SP?

This is my actual code:

 public static void Import(string username, string domain,string completeDomain)
    {
        PrincipalContext ctx = new PrincipalContext(ContextType.Domain, completeDomain);
        Console.WriteLine(ctx.Name + " --> " + ctx.UserName + " --> " + ctx.ConnectedServer);
        Console.ReadKey();

        UserPrincipal findAllUser = new UserPrincipal(ctx); 

        PrincipalSearcher ps = new PrincipalSearcher(findAllUser);

        try
        {
            Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(delegate()
                 {
                     using (SPSite elevatedSite = new SPSite(GetUrl()))
                     {
                         using (SPWeb web = elevatedSite.OpenWeb())
                         {
                             foreach (Principal user in ps.FindAll())
                             {
                                 web.AllowUnsafeUpdates = true;
                                 elevatedSite.AllowUnsafeUpdates = true;

                                 Console.WriteLine(user.Name + "-->" + user.DistinguishedName);
                                 Console.ReadKey();

                                 var loginName = domain + "\\" + user.SamAccountName;
                                 var name = user.DisplayName;
                                 web.AssociatedVisitorGroup.Users.Add(loginName, string.Empty, name, string.Empty);

                             }
                         }

                     }
                 });
        }
        catch (Exception exx)
        {
            Console.WriteLine(exx.Message);
            Console.WriteLine(exx.StackTrace);
            Console.ReadKey();
        }
        Console.ReadLine();
    }

Answer 1

If you just want to add all users, just add NT AUTHORITY\authenticated users

If you want to add every user individually, you have to get users (maybe as Principals) from AD, and add them to a group in SharePoint.

var principal...
var loginName = @"MYDOMAIN\" + principal.SamAccountName;
var name = principal.DisplayName;
web.AssociatedMemberGroup.Users.Add(loginName, "", name, "");