Is there any way to give all users access to one blog in a multisite network without using a plugin?

Question

I know there are various plugins out there to help with multisite user management, but we have a policy of avoiding plugins for a) overzealous security policies, and b) interfering with our already heavily-modified WordPress installation (this has bit us before).

Also, simply adding all ~10,000 users to this one blog seems inelegant. That's a lot of new entries in wp_usermeta.

Is there any filter or action I can intercept to say "if this is blog X, then let any registered user through"? The admin_init action hook lets me restrict users according to arbitrary criteria, but I don't know how to let them through.

Answer 1

You could filter get_blogs_of_user and add this particular blog to the returned list. Pseudo-code, not tested:

add_filter( 'get_blogs_of_user', 'add_special_blog', 10, 3 );

function add_special_blog( $blogs, $user_id, $all )
{
    $new_blog = get_blog_details( $special_blog_id );

    $blogs[ $special_blog_id ] = (object) array(
    'userblog_id' => $special_blog_id,
    'blogname'    => $new_blog->blogname,
    'domain'      => $new_blog->domain,
    'path'        => $new_blog->path,
    'site_id'     => $new_blog->site_id,
    'siteurl'     => $new_blog->siteurl,
    'archived'    => 0,
    'spam'        => 0,
    'deleted'     => 0
    );

    return $blogs;
}