JWT verification in production: an 8-check field guide

A correct JWT verifier does eight things. Most production verifiers I have read do four or five of them. The other three or four get skipped because the library defaults aren't loud about them, the docs gloss over them, or someone copied a "it works" snippet from Stack Overflow circa 2018. Here is the full eight-check list, what each one prevents, and what it looks like to implement them with structured error codes — the kind that survive a midnight 401 incident with a clear remediation path. 1.