C++ is unique in that it is wildly dominant in its niche. I am sure that any developer who has worked with another object oriented, manually memory managed, systems programming language (are there any other popular ones out there?) should have no trouble picking up C++.
Did you remember to plan for a zero downtime encryption key rotation?
Did you know when account passwords expire? Have you thought about password rotation?
That sounds like a good practice until you have 20 (or even 2000) backend server requests per end user operation.
All of those are taken from my experience.
Security is like an invasive medical procedure: it is very painful in the short term but prevents dire complications in the long term.