Security is not a feature you add at the end. In the systems we run, it is a set of habits applied to every change, every day.
Every account has a role, and every role sees only what it needs. Passwords are hashed, sessions expire, and sensitive actions are written to a log that cannot be quietly edited. Forms are protected against forged requests and automated abuse; uploads are checked before they are stored.
We keep secrets out of code and out of chat, rotate them when people or suppliers change, and keep backups that we have actually tried to restore. When something looks wrong, we would rather take a feature offline for an hour than leave a door open.
We are also careful about what we publish. A public website should explain what a product does, not how its defences are built. Detailed security documentation is shared with customers under agreement.
None of this is glamorous. It is simply what it takes to run software that businesses trust with their customers.