You need a really secure authorization, a third-party service or your own! How and where?

Question

User identification

Hello!
I reviewed my different scripts and there are always some security nuances somewhere, I don’t want to use something from OpenSour because it needs to be updated and added regularly, and the best hole is the one that they don’t know about. I think that this solution has a lot more of them since it is open, and is already being finished after hacking, this is my opinion, maybe I don’t know much.
I need a site with my own or third-party authorization, login password, when authorizing, a personal account with differentiation of rights and connection of any functionality, depending on the user.
Tell me what is now out of this, how much it can cost, it’s easier to buy a ready-made one, or place an order for writing such a script. Thank you!