To authenticate your users against an existing FTP server, edit and add a line like this:
::ftp=ftpserv.mylib.org
Replace "ftpserv.mylib.org" with the appropriate host name for the FTP server. This change takes effect immediately, without the need to restart EZproxy. When EZproxy receives authentication requests, it will attempt to connect to the FTP server, and if the FTP server indicates login success, then the remote user will be authenticated and allowed to proceed.