Identity, Authentication & Authorization Separate who the caller is from what the caller may do
Phase 16 - Authentication Fundamentals Volume 05 - Authentication & Security
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Phase 16 builds the security mental model before any Supabase Auth integration code is introduced.
Identity is not the same thing as authentication A useful security model starts by naming different concepts precisely. "User", "login", "JWT", and "permission" are not interchangeable terms.
Credential / Evidence used to authenticate password, passkey, OTP, security key authenticator
Authorization (AuthZ) Decide what the identity may do may edit this Task?
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Authentication establishes who; authorization decides what that authenticated subject may do.
Identification alone is not proof Typing an email address tells the system which account you claim to be. It does not prove you own that account. Likewise, sending userId=123 from a browser does not prove you are User 123.
# Wrong trust model GET /tasks?userId=123
# Browser says who it wants to be. # The API has no authentication proof.
The trust-boundary rule Anything the browser can freely choose is untrusted input. Identity becomes trusted only after the backend verifies an authenticator or a token issued by an identity system it trusts.
Never derive authorization from a user ID, email, role, or permission value merely because the browser sent it.
Authentication vs authorization failure Situation Typical meaning
No valid authentication 401 Unauthorized (historical HTTP name; semantically unauthenticated)
Authorization decides what an authenticated identity may do to a specific resource. UI hiding is never a substitute for server-side enforcement.
Restate the goal of “Identity Authentication and Authorization” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: trusted identity → requested action → resource scope → policy decision → allow/deny. Mark the one boundary this lesson changes.
Inspect the current repository state and record the exact files, route, table, or runtime involved. Avoid creating an abstraction before you can name the existing owner.
Implement the smallest vertical slice. Add one coherent change, run the narrowest verification command, and read the output before continuing.
Connect the slice to TaskFlow’s phase artifact: Authentication threat/flow diagram explaining what the browser stores, what servers verify, and what happens when credentials expire.. Verify behavior from the outside as a user or API client would.
Create one controlled failure that is safe to reproduce. Predict the symptom first, capture evidence, locate the earliest broken boundary, then fix only that cause.
Close the reference and rebuild or explain the core change from memory. Record what you would monitor or test before trusting the same change in production.
const canEdit =
user.role === "ADMIN" ||
(user.role === "MEMBER" && task.ownerId === user.id);
if (!canEdit) throw new ForbiddenException();Do not copy this as a finished answer. Predict what each boundary does, type the smallest useful slice, run it, then compare the result with your prediction.
Trace verified identity, role, resource owner/workspace, and policy inputs separately.
Add server-side resource authorization; UI visibility is only experience, never enforcement.
Without copying the final source, create a second small scenario that applies “Identity Authentication and Authorization” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Draw password login without writing code and mark where plain-text password may exist temporarily.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Treating base64 JWT content as proof of authenticity
Predict the symptom before causing the failure. Then locate the earliest boundary where reality diverges from expectation.Why does this responsibility live here, what input does it trust, what output proves success, and what would go wrong if another layer owned it?
If your explanation is vague, repeat the boundary trace before moving on.Close the reference. Reproduce the core idea from memory or explain the exact request/data flow aloud. Then check your diff or notes for accidental shortcuts that bypass validation, authorization, error handling, or verification earned in earlier phases.