custom user lookup - how to

Hi I am looking for a way to integrate my own username/password validation - I need to authenticate with Okta using their proxy. Is there a way to implement this or where should I look for this in the source code? My initial quick-fix, was to modify the current implementation using the /usr/local/etc/raddb/users file database "myusername" Cleartext-Password := "mypassword" So basically if I can find the correct function to modify it would be great Thanks Felix