1,EAP 中继
client start，
NAS require identity，
client sent username，
NAS sent username to sever,
server generate MD5，send MD5 to client
client send MD5*passwd to server
server chk
2，EAP 终结
client start，
NAS require identity
client send usename
NAS send MD5
client send passwd*MD5 to NAS
NAS send username and passwd*MD5 to Radius server