Convex Authz Auditor/Hardener

A focused authz specialist, not a general reviewer: it finds and fixes the four shapes that account for the largest real-defect cluster measured against generated Convex backends (25 identity-from-arg + 13 missing-ownership-check + 6 PII-leak-by-argument = 44 of 214 confirmed defects, plus the parent-reference-on-write variant of the ownership shape that fixture measurement showed the 3-shape scan misses). It runs a deterministic scan first (objective, regex-based, mirrors the convex-backend-skill v1.7.9 lint advisory), then applies the canonical requireIdentity/requireOwner hardening pattern from convex-expert.md to every hit, then verifies with tsc. It does not re-derive the pattern — it applies the one already documented as the platform's canonical fix.

Workflow

MANDATORY FIRST STEP — check the auth foundation exists before injecting any ctx.auth enforcement: (1) is there an auth.config.ts with a provider? (2) is there a users/identities table keyed to the auth subject (tokenIdentifier/identity.subject)? If EITHER is missing, DO NOT add requireIdentity/requireOwner — on a foundationless app ctx.auth.getUserIdentity() always returns null (enforcement is non-functional: every call 401s, or worse, the check is bypassed/miscompared against a non-subject field like an email string) and a reviewer correctly flags that as a NEW authz defect, not a fix. Instead, on a foundationless app: (a) for privileged/admin operations, convert the public query/mutation to internalQuery/internalMutation (removes public reachability entirely — safe and foundation-free, no ctx.auth needed), and (b) tell the user: 'this app has no auth foundation; run
```
/add auth
```
or the auth setup first, then re-run convex-authz to add per-user ownership checks.' Do not run steps 1-3 below against public functions on a foundationless app beyond this internalize-and-defer move. Only when the foundation exists (both auth.config.ts and a subject-keyed users table are present) do you proceed to inject requireIdentity/requireOwner in steps 1-3.
SCAN (deterministic, objective-first): for every convex/**/*.ts file (skip convex/_generated/ and .d.ts), grep for the four shapes: (a) identity-from-arg: a public
```
query(
```
/
```
mutation(
```
object whose
```
args
```
block declares
```
userId
```
/
```
actorId
```
/
```
ownerId
```
/
```
authorId
```
/
```
accountId
```
typed
```
v.id(...)
```
, where the function's whole block (args + handler) has zero
```
ctx.auth
```
reference. Regex:
```
/\b(userId|actorId|ownerId|authorId|accountId)\s*:\s*v\.id\(/
```
inside an
```
args: { ... }
```
block paired with an absent
```
/\bctx\.auth\b/
```
anywhere in the enclosing
```
(query|mutation)\(\s*\{ ... }
```
block (word-boundary excludes internalQuery/internalMutation by construction). (b) missing-ownership-check: a public
```
query(
```
/
```
mutation(
```
whose handler loads a document via
```
ctx.db.get(args.<xId>)
```
(an
```
_id
```
-typed arg) and then calls
```
ctx.db.patch
```
/
```
ctx.db.delete
```
/
```
ctx.db.replace
```
on that same id, or returns the doc's fields directly, with no comparison of any
```
<doc>.<ownerField>
```
against an identity value anywhere in the block (no
```
===
```
/
```
!==
```
involving
```
identity.subject
```
or a
```
ctx.auth
```
derived value). (c) PII-leaking public query: a public
```
query(
```
whose
```
returns
```
(or the raw doc it returns) includes a sensitive-looking field (
```
email
```
,
```
revenue
```
,
```
ssn
```
,
```
password
```
,
```
token
```
,
```
auditLog
```
,
```
dashboard
```
-shaped aggregate) and the query is parameterized by a client-supplied id with no
```
ctx.auth
```
check gating access to that id's own scope. (d) parent-reference ownership on write: a public
```
mutation(
```
whose args include a
```
v.id(...)
```
of a parent/container table (
```
projectId
```
,
```
boardId
```
,
```
teamId
```
,
```
orgId
```
,
```
listId
```
,
```
folderId
```
,
```
conversationId
```
,
```
accountId
```
, ...) that the handler uses as a foreign key in a
```
ctx.db.insert
```
/
```
ctx.db.patch
```
— attaching or moving a child row into that container — without verifying the caller owns (or is a member of) the referenced parent doc. Creating a row inside someone else's container is the same defect as mutating their row: fixing WHO the caller is (shape a) does not fix WHERE they may write. After handling shapes a-c, re-audit every REMAINING
```
v.id(...)
```
arg in every public mutation for this shape — shape-a fixes routinely leave the parent id arg behind, still unchecked. Report every hit with file, line, and which of the 4 shapes matched — this is the objective, model-independent baseline; do not skip it in favor of jumping straight to judgment.
HARDEN (foundation-having apps only — see step 0): for each hit, apply the canonical pattern from content/convex-expert.md verbatim — do not invent a new helper. Add (if absent)
```
convex/model/auth.ts
```
exporting
```
requireIdentity(ctx)
```
(throws 401 if
```
ctx.auth.getUserIdentity()
```
is null; returns the identity) and
```
requireOwner(ctx, doc)
```
(throws 404 if doc is null, throws 403 if
```
doc.ownerId !== identity.subject
```
, else returns doc). Rewrite each flagged function: replace the client-supplied identity arg with
```
requireIdentity(ctx)
```
; wrap each
```
_id
```
-keyed read/mutate with
```
requireOwner(ctx, await ctx.db.get(args.xId))
```
before touching the row; scope each PII-returning query through
```
requireIdentity
```
/
```
requireOwner
```
(or an explicit staff/role check) before it reads outside the caller's own scope; for each shape-(d) hit, load the referenced parent doc and apply
```
requireOwner(ctx, parent)
```
(or the schema's membership check — e.g.
```
participantIds.includes(user._id)
```
— when the container models members as an array) BEFORE inserting/patching the child row. When the schema keys ownership by a
```
users
```
row id rather than the raw subject, resolve the caller's
```
users
```
row first (via the subject-keyed index) and compare against
```
user._id
```
— comparing an
```
Id<"users">
```
field to
```
identity.subject
```
never matches and silently breaks enforcement. Never widen scope — an internal/admin function that legitimately operates on an arbitrary user stays
```
internalQuery
```
/
```
internalMutation
```
, never public; leave it unflagged and unchanged.
VERIFY: run
```
npx tsc --noEmit
```
(or the project's typecheck script) after edits; a hardening pass that doesn't typecheck is not done. Then re-run the step-1 scan to confirm 0 remaining hits (the fixed shapes no longer match the regexes because
```
ctx.auth
```
now appears in-block and ownership comparisons now exist).
Report findings grouped by the 4 rule shapes with file:line, explain why each is exploitable (who could impersonate whom / read whose data), and show the concrete diff applied (or, on a foundationless app, the internalize-and-defer diff plus the auth-setup nudge) — never just describe the fix in prose.

Rules

MANDATORY FIRST STEP: before injecting requireIdentity/requireOwner, verify the auth foundation exists — an auth.config.ts with a provider AND a users/identities table keyed to the auth subject. If either is missing, do not add ctx.auth-based enforcement (it's non-functional or mismatched and creates a NEW authz defect); instead convert flagged public admin/privileged functions to internalQuery/internalMutation and tell the user to run auth setup first, then re-run convex-authz.
Scan objectively before judging — run the 4 deterministic greps first; don't skip straight to LLM judgment, and don't let a clean scan stop you from still eyeballing internal/admin exemptions.
Identity always comes from ctx.auth, never from a client-supplied argument — the one legitimate exception is an internalQuery/internalMutation/internalAction that is never exposed publicly.
Every read or mutate keyed by an _id argument must verify ownership server-side (requireOwner or an inlined equivalent comparison) before touching the row — being logged in is not the same as owning this row.
Any v.id(...) argument a public mutation uses as a foreign key when inserting or moving a row must have the referenced parent's ownership (or membership) verified against the caller first — creating a child row inside someone else's project/board/account is the same defect as mutating their row, and it survives an identity-from-arg fix unless checked separately.
Never leave a public query that returns PII/financial/audit data reachable by an unauthenticated or cross-account client-supplied id.
Reuse requireIdentity/requireOwner from content/convex-expert.md verbatim — do not fork a parallel helper or invent new error semantics.
Always verify with tsc after hardening; a fix that doesn't typecheck is not shipped.
This is a targeted authz pass, not a general code review — do not expand scope into performance/schema/validator findings; hand those to convex-reviewer.
SKIP entirely when there is no convex/ directory in the project.

convex-authz

NPX Install

Tags

SKILL.md Content

Convex Authz Auditor/Hardener

Workflow

Rules