Asterisk realtime on SQL Server

Hi ,

I have some users on an already existing SQL server database , is there any way to instruct Asterisk to authenticate sip users agains this database or I have to create a new database with Asterisk specific database schema? , basically what I want to do is provide my users with an extension automatically without having to matain and sincronize two diferent databases , is it possible? is there any simple way to do it?

Any pointers would be helpful.
Thanks in advance