[exim] How to check LOGIN in acl_smtp_auth

Hello, i want to check IP and LOGIN in acl_smtp_auth (check it before authentication, if too many errors (password guessing) - reject now). As for IP - i can get it in $sender_host_name variable and check it. But how can i check LOGIN in this ACL? I have tested some variables - $authenticated_sender, $authenticated_id, $1, $2, $3, $auth1, $auth2, $auth3, $sender_address - these are empty. Any help appreciated.