SQL - How to use MSSQL for Authentication and MySQL for Accounting

Greetings, I have searched for some time but cannot seem to find an answer to this, but I am sure it can be done. I use a MSSQL database on a separate server for Authentication and that is working well. I want to use a MySQL database on a third server for Accounting. Everything I have searched shows how to configure it for one or the other but not both. I am trying to find out how to accomplish this, so if anyone has some insight, please do share. Thanks in advance. Jer