MSSql database data writing and retrieving

Hi everyone, I’m developing a website for a company that use a MSSql database to manage subscription fees and personal details of their clients. I’ve searched between plugins that allow WP to interact with an external MSSql DB, but it seems to be nothing specific except one that permits users authentication, so I decided to develop by myself both Front-end and Back-end required functions. Is there anyone that could recommend me tutorials or resources to get started?