The third case is very common. I would not even use the word "refuse" Sometimes the legacy system is so legacy that fixing it is a many years project. Sometime

The third case is very common. I would not even use the word "refuse" Sometimes the legacy system is so legacy that fixing it is a many years project. Sometimes you have such a messy environment that rotating credentials means a general crash. Sometimes you have legacy software that must stay legacy and you cannot patch + that software is so ingrained into your system that you cannot isolate it. Sometimes ... This is all bad design and bad architecture from scratch. Or "good architecture 25 years ago".