server config, <VirtualHost>, <Global>
1.0.3/1.1.1 and later
AuthGroupFile specifies an alternate groups file, having the same format as the system /etc/group file, and if specified is used during authentication and group lookups for directory/access control operations. The path argument should be the full path to the specified file. AuthGroupFile can be configured on a per-VirtualHost basis, so that virtual FTP servers can each have their own authentication database (most often used in conjunction with AuthUserFile).
Note that this file need not reside inside a chroot()ed directory structure for Anonymous or DefaultRoot logins, as it is held open for the duration of client connections.