Secure Development of iOS and macOS Applications

Many app owners and developers don’t realise that their apps may be full of threats. Those vulnerabilities are waiting for an average hacker right in the AppStore. An average hacker doesn't even need access to the source code to find and exploit bad mistakes.
It appears that secure mobile development is not commonly practiced even nowadays, that’s why we will also look at some techniques to avoid those pretty disappointing mistakes during app development.
The tips here are in no particular order, however, first half of instructions is more important that another. If a developer team manages to implement at least 50% of these tips, then their app will be 99% protected against crime.