How to add programmatically "every user" group to a Sharepoint Site

Question

I'm trying to add a group that contains every user on my SharePoint application.

How would I do this?

I tried to get the BUILTIN\users or the NT Authenticated\Authenticated users from the SPWeb.SiteGroups[name]...

If I add BUILTIN\users from SP GUI it works... Is there something I need to enable to do that? I need to have a document library in which every user (10,000) can contribute... Are there other ways?

Thank you

Answer 1

You can get all authenticated users like below

SPUser allusers = web.EnsureUser("NT AUTHORITY\\authenticated users");