MSCHAP Combining AD Authentication with External Script

Hi FreeRADIUS People, I want to combine AD Authentication with my external script. I know it's not recommended to use an external script but I have to use that.. In my external script, basically I'm providing the cleartext-password to FreeRADIUS if the username is correct. I'm trying to working with two scenarios; 1. Try to authenticate first using the external script, if this script returns reject, this time try with authentication with the AD. 2. Try to authenticate first using the AD server, if the AD server returns reject, this time try with the external script. Thanks in advance,