plain-text password not get with CHAP

Respected All, I using Default *Auth-Type = Accept* and *php external script* for custom authentication. That is working fine with only pap in PPPoE, But not working with CHAP, MS-CHAPv2 etc. I found one reason was the external script not get the plain-text password.Usually i get password in external php script with *trim(getenv('USER_PASSWORD'),'"'); *this env variable. So, any way to get plain-text password in external script when chap is on in mikrotik? Warm regards Imdadali Kadiwala