Even if you learnt how to do this stuff, and you were able to implement it correctly and securely (and as I wrote above, it’s not nearly as straightforward as you make it sound like)…

Even then, authentication is unlikely a core part of your app. Your team should use your time as developer (which is very expensive) to work on features that actually add value to the business. Authentication almost never does.

And what about live site issues? Isn’t it better if there’s another company taking care of those rather than having to pay your own employees for that?