Authentication versus authorization
By the end of today you can separate proving who someone is from deciding what they may do, and spot the authorization bug where an endpoint checks the first and forgets the second.
YesterdayOn Day 37 you learned to validate what data is. Today you validate who is sending it and whether they may.
TomorrowTomorrow, the mechanics: how a server remembers you across stateless requests.
Why this matters
Broken authorization is consistently among the most common serious vulnerabilities in real systems, and it is almost always the same mistake: checking that someone is logged in and forgetting to check whether the record is theirs.
- Authentication
- Authorization
- Object-level authorization
- Least privilege
Learn it
75 minCopy this into Claude or ChatGPT. It quizzes you before it explains anything, which is deliberate. The resources under it are how you check what it told you.
Today's Master Prompt
Free · sign inA prompt written for this day alone: your level, the exact scope, what to leave out, and an instruction to quiz you before it explains anything. Paste it into Claude or ChatGPT and it teaches you today's material.
Check it against something that is not a model
An assistant can be fluent and wrong, and on a topic you met today you will not catch it. These cover the same ground and were made by people who do this for a living, so they are what you hold the explanation up against. They are other people's work and we only link to them, so judge them for yourself.
3 hand-picked resources
Free · sign inVideos, official docs and articles covering the same ground, each opened and annotated by hand. They are what you check the assistant against on a day you cannot yet catch it being wrong.
Build it
45 minAdd a user concept to your books API so each book has an owner. Write an endpoint that fetches a book by ID with only an authentication check, then attack it by requesting another user's book. Fix it with an ownership check, and then write down every other endpoint that needs the same fix.
Recall it
20 minAnswer out loud, reveal, then mark honestly whether you had it. That score is the only thing on this page you do not get to choose.
5 recall questions
Free · sign inQuestions you answer from memory, then grade yourself against the real answer. The score is carried into the mastery rating below it, so an honest miss cannot quietly become a tick.
Rate it
Completion and mastery are tracked separately. Be honest, because an inflated rating only means the concept resurfaces sooner.
Mastery tracking
Free · sign inRate yourself against five named criteria per concept. Completion and mastery are tracked separately, and anything you rate shakily comes back automatically on a spaced schedule.
Recap
- 01Authentication is who you are; authorization is what you may do
- 02Checking login without checking ownership is the most shipped auth bug
- 03Checks belong in the service layer, where they cannot be forgotten
- 04An unlinked URL is not a security control
Your progress
Free · sign inMark days complete, pick up where you left off across devices, and watch completion and mastery diverge. Free, and the account exists only so ninety days of work cannot vanish with a cleared browser.