PPTP authentication via Debian user accounts

I've set up pptp vpn on Debian. Works fine. User authentication is made base on file /etc/ppp/chap-secrets.

I'm looking for option that user authentication in pptp would be made base on debian system users accounts or samba accounts at last. Ther's no clue on google or forums so I decided to write a post.
It's not very comfortable when I must add ordinary users to debian system (eg. to provide them ftp or samba accounts) and then add new users to pptp user file.

I would be very thankfull for point me to solution. Thank you in advance.

This above question was posted by me in "Unix 4 dummies" thread. But for few days is remain with no answer. It might by to hard to answer or to dummie also - I don't know - so I decided to move it to Expert thread. Once again - I would be very thankfull for point me to solution. Thank you in advance.