How to validate user credential to unix ftp server

Question

Hi,
For our project we are using Solaris box.
After our build completion we keep kits to one directory and let users to access it by FTP session.
So we create user account on Solaris and share this info. to respective group of user.

I want to change this part and implement it like, 1.- Let user to login to ftp server with its one of the property login as 'anonymous' ... but change is, user/password = 'anonymous/@client-server'
2.- When user login as 'anonymous' run some script to check for its password. Based on that update this to log file.

The main idea is to avoid creating new user on server and by just validating password, can process which user has logged in.

So is it possible to run any script on server when any user logged in through FTP server?

Thanks in advance.