Im here again sire.
Just clearing things up a little bit.

I have multiple VPN server which currently uses individual authentication system built within each of them.
I am wondering how can I use a central authentication system for all my VPN so one specific client
can access all my server using only a single authentication system.
If you can give me some codes or external reference it would greatly help me a lot.
Please guys im really in need of this... please help me.
Thanks.