diff --git a/.changeset/adr-0056-form-self-auth.md b/.changeset/adr-0056-form-self-auth.md
new file mode 100644
index 0000000000..5cdcf67653
--- /dev/null
+++ b/.changeset/adr-0056-form-self-auth.md
@@ -0,0 +1,20 @@
+---
+"@objectstack/plugin-security": minor
+"@objectstack/rest": patch
+---
+
+feat(security): declaration-derived public-form authorization (ADR-0056, Option A)
+
+Public form submissions are now authorized by the **declaration**, not by a
+deployment-configured `guest_portal` profile. The form-submit route derives a narrow
+`publicFormGrant: { object }` from the matched form's target object; the SecurityPlugin
+honors it as a least-privilege capability — **create + the immediate read-back on THAT
+object only**, with no userId, and crucially NOT the anonymous fall-open. This makes
+public forms work under secure-by-default (`requireAuth`) **without** a hand-configured
+`guest_portal`, scoped to exactly the declared object (the field allow-list is still
+enforced at the route; `guest_portal`/`anonymous` are kept on the context for back-compat
+with guest-detection hooks). It is the prerequisite that unblocks the eventual
+`requireAuth` default flip, and generalizes the platform principle "public access =
+declared + runtime-derived scoped grant" (the same shape share-links already use).
+Proven by `form-self-auth` dogfood (create on target allowed; cross-object + update/delete
+denied). plugin-security 108, rest 121, full dogfood 98 — no regression.
diff --git a/packages/dogfood/test/form-self-auth.dogfood.test.ts b/packages/dogfood/test/form-self-auth.dogfood.test.ts
new file mode 100644
index 0000000000..6fbb7c9688
--- /dev/null
+++ b/packages/dogfood/test/form-self-auth.dogfood.test.ts
@@ -0,0 +1,53 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+//
+// ADR-0056 (Option A) — declaration-derived public-form authorization.
+// A public form submission carries a `publicFormGrant: { object }` derived from
+// the form's declared target. The SecurityPlugin honors it as a NARROW capability:
+// create + read-back on THAT object only — no userId, no deployment-configured
+// `guest_portal`, and crucially NOT the anonymous fall-open (which would allow
+// anything). This is what lets public forms survive a secure-by-default flip
+// while staying least-privilege. Proven at the engine boundary (the same
+// middleware the HTTP form-submit route flows through).
+
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import showcaseStack from '@objectstack/example-showcase';
+import { bootStack, type VerifyStack } from '@objectstack/verify';
+
+const idOf = (r: any) => r?.id ?? r?.record?.id ?? r?.data?.id ?? r;
+
+describe('ADR-0056 Option A — public-form grant (declaration-derived)', () => {
+  let stack: VerifyStack;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  let ql: any;
+
+  beforeAll(async () => {
+    stack = await bootStack(showcaseStack);
+    await stack.signIn();
+    ql = await stack.kernel.getServiceAsync('objectql');
+  }, 60_000);
+
+  afterAll(async () => { await stack?.stop(); });
+
+  it('authorizes CREATE on exactly the declared object (no userId / no guest_portal)', async () => {
+    const ctx = { publicFormGrant: { object: 'showcase_private_note' } };
+    const r = await ql.insert('showcase_private_note', { title: 'from public form' }, { context: ctx });
+    expect(idOf(r), 'create on the form target succeeds').toBeTruthy();
+  });
+
+  it('is NARROW — does NOT extend to other objects (not the anonymous fall-open)', async () => {
+    const ctx = { publicFormGrant: { object: 'showcase_private_note' } };
+    await expect(
+      ql.insert('showcase_announcement', { title: 'cross-object' }, { context: ctx }),
+      'grant for private_note must not authorize announcement',
+    ).rejects.toThrow();
+  });
+
+  it('does NOT permit update/delete (create + read-back only)', async () => {
+    const seed = await ql.insert('showcase_private_note', { title: 'seed' }, { context: { isSystem: true } });
+    const ctx = { publicFormGrant: { object: 'showcase_private_note' } };
+    await expect(
+      ql.update('showcase_private_note', { id: idOf(seed), title: 'hacked' }, { context: ctx }),
+      'grant must not authorize update',
+    ).rejects.toThrow();
+  });
+});
diff --git a/packages/plugins/plugin-security/src/security-plugin.ts b/packages/plugins/plugin-security/src/security-plugin.ts
index 869d28142a..7aee1c1369 100644
--- a/packages/plugins/plugin-security/src/security-plugin.ts
+++ b/packages/plugins/plugin-security/src/security-plugin.ts
@@ -285,6 +285,28 @@ export class SecurityPlugin implements Plugin {
         return next();
       }
 
+      // ADR-0056 (Option A) — declaration-derived PUBLIC-FORM grant. A public
+      // form submission carries `publicFormGrant: { object }` derived from the
+      // form's declared target (set by the rest-server form-submit route). It
+      // authorizes ONLY create + the immediate read-back on THAT object — never
+      // anything else, and never the anonymous fall-open. This lets public forms
+      // work under secure-by-default (requireAuth) WITHOUT a deployment-configured
+      // `guest_portal`, scoped to exactly the declared object (the field
+      // allow-list is enforced at the route; the context is request-scoped).
+      const formGrant = opCtx.context?.publicFormGrant;
+      if (formGrant && typeof formGrant === 'object' && (formGrant as { object?: string }).object) {
+        const grantObject = (formGrant as { object: string }).object;
+        const allowed =
+          opCtx.object === grantObject &&
+          ['insert', 'find', 'findOne', 'count'].includes(opCtx.operation);
+        if (allowed) return next();
+        throw new PermissionDeniedError(
+          `[Security] Access denied: public-form grant permits only create/read-back on '${grantObject}', ` +
+            `not '${opCtx.operation}' on '${opCtx.object}'`,
+          { operation: opCtx.operation, object: opCtx.object },
+        );
+      }
+
       const roles = opCtx.context?.roles ?? [];
       const explicitPermissionSets = opCtx.context?.permissions ?? [];
 
diff --git a/packages/rest/src/rest-server.ts b/packages/rest/src/rest-server.ts
index baba2cf9a0..50e741135b 100644
--- a/packages/rest/src/rest-server.ts
+++ b/packages/rest/src/rest-server.ts
@@ -3708,12 +3708,15 @@ export class RestServer {
                         Object.assign(filteredData, rawBody);
                     }
 
-                    // Anonymous execution context. Carries the `guest_portal`
-                    // permission set name so the SecurityPlugin resolves it
-                    // and enforces INSERT-only on the target object.
-                    // Leaving `userId` undefined keeps `ctx.user?.id` falsy
-                    // in object hooks (the canonical guest-detection check).
+                    // ADR-0056 (Option A): authorization DERIVED from the declared
+                    // form — a narrow create grant scoped to exactly this form's target
+                    // object. The SecurityPlugin honors `publicFormGrant` (create + the
+                    // immediate read-back, that object ONLY), so public forms work under
+                    // secure-by-default (requireAuth) WITHOUT a deployment-configured
+                    // `guest_portal`. `guest_portal` + `anonymous` are kept for back-compat
+                    // with object hooks (guest detection via falsy `ctx.user?.id`).
                     const context: any = {
+                        publicFormGrant: { object: match.object },
                         permissions: ['guest_portal'],
                         anonymous: true,
                     };