Linux and Unix server administration, MySQL database experience, PHP & BASH programming, with a wide array of web technology understanding (networking, DNS, etc).
I have created many custom built applications using PHP. These include stand alone and multi-user database systems. I have advanced knowledge on setting up the servers behind the software such as Linux, DNS, TLS/SSL, SSH, MySQL database server, etc.
It is unfortunate I didn't join earlier as I could probably assist with this scope of work. It would come down to your current system layout.
I have programmed many multi-user systems that interact with MySQL. One would need to make sure passwords are stored in a safe manner.