Review the fix (secure code review)

An ordinary system diagram redrawn with every door marked. A code review is that drawing done at the scale of one change: find the door the change touches, and follow what comes through it.

Before you start. The Security Mindset gave you the trust boundary: the line a request crosses when it comes from someone you do not control. Lessons Authentication to Application Hardening, and Whose page is this? (the browser security model), each taught one defence at one door (a salted slow hash, an ownership check, a bound parameter, an escaped character, an allowlist, the origin rule). This lesson puts them together as twelve short pieces of real code, already fixed, and asks you to read each one the way a reviewer does.