import bitel.billing.server.radius.*;

prefix = "ppp";
login = request.getStringAttribute(RadiusStandartAttributes.User_Name);
int count = login.length();

if (login != null && count == 5) {
   request.setStringAttribute(RadiusStandartAttributes.User_Name,prefix+login);
}

10 21:01:31
Type=AUTHENTICATION_REQUEST
Attributes:
User-Name=ppp12345
NAS-Identifier=nas.domen.lan
NAS-IP-Address=10.0.5.254
Tunnel-Type=
NAS-Port=1
Tunnel-Medium-Type=
Service-Type=2
Tunnel-Client-Endpoint=10.0.5.36
Framed-Protocol=1
Tunnel-Server-Endpoint=10.0.5.254
Acct-Session-Id=1537553-PPTP-1
NAS-Port-Id=rl2
Tunnel-Server-Auth-ID=nas.domen.lan
NAS-Port-Type=5
Calling-Station-Id=10.0.5.36
mpd-link=PPTP-1
MS-CHAP2-Response=\u1\u0Z\???RvV?
???\u17\u28?\u0\u0\u0\u0\u0\u0\u0\u0!??lY???8¦\u12?\u11d#?\u5??°Pi\u29U
MS-CHAP-Challenge=»\u30hm@??p\u15P?;?\u250~

10 21:01:31
Type=AUTHENTICATION_REJECT
Process time auth: 34 common_auth: 6
Attributes:
Reply-Message=2