I don't see any indication in the post that these cases involved someone writing their own authentication code. This is about authorization mistakes, or the lack of any authorization. And that part you have to write yourself in some way (even if you use libraries), someone has to define the rules about which data is accessible under which rules. Using a pre-made library won't save you from defining those rules wrong.

To me only hard rule like this is to never implement your own cryptographic code. A decent developer can easily implement simple session-based authentication safely, or at least I'd suspect the chance of mistakes is no higher than this developer misconfiguring a much more complex library for authentication.