- Write some tests to verify that things work as you think they should.
- Identify potential security threats.
- Write a test for each one.
The process isn't very difficult once you get started. I suspect, though, that, given your history, you're not going to do much research on your own and, instead, are going to ask a bunch of questions here and not really work hard at getting to the meat of the answers. Honestly, if I were in your shoes, I would hire someone to do the work and you look over their shoulder. That way, it gets done properly and you have a reference implementation to look back at when you go to your next project.
My criteria for good software:
- Does it work?
- Can someone else come in, make a change, and be reasonably certain no bugs were introduced?