@@ -0,0 +1,19 @@
+---
+'@objectstack/plugin-auth': patch
+---
+
+fix(plugin-auth): an MCP client that registers over OAuth dynamic client registration with a loopback or custom-scheme redirect, and no `application_type`, is registered as a native client instead of being refused
+
+Clause-②: no (a runtime security-boundary change the maintainer ruled; no published type, export or metadata key moves)
+Metadata-protocol: none
+
+Local MCP clients (Claude Code, Cursor, VS Code, Codex CLI) register at `POST /api/v1/auth/oauth2/register` with a loopback `http` redirect (`http://localhost:PORT/...`, `http://127.0.0.1:PORT/...`) or a custom-scheme redirect, and send no `application_type`. The OAuth provider used to fill the missing type with `web` and refuse both redirect forms (`invalid_redirect_uri: web clients require https redirect URIs on non-loopback hosts`), so these clients could not connect to the MCP endpoint over OAuth and API keys were the only working path.
+
+plugin-auth now passes `clientRegistrationDefaultApplicationType: 'infer'` to `@better-auth/oauth-provider`. A dynamic registration that omits `application_type` is classified `native` when any redirect URI uses a non-http(s) scheme or `http` on exactly `localhost`, `127.0.0.1` or `[::1]`, and every redirect URI is then validated by the native rule. Otherwise it stays `web`. What this changes and what it keeps:
+
+- Accepted as `native`: the body a local MCP client sends (a public client with a loopback or custom-scheme redirect).
+- Unchanged: an `application_type` the client sends is never overridden; `https://example.com/cb` alone stays `web`; `http://example.com/cb` and `http://localhost.example.com/cb` stay refused; with dynamic client registration off, every registration is still refused.
+- Also accepted as `native`: a confidential registration (`client_secret_basic`, or no `token_endpoint_auth_method`, which the provider fills as `client_secret_basic`) with a loopback or custom-scheme redirect and no `application_type`, which is issued a `client_secret`. The same body was already accepted with `application_type: 'native'` spelled out, so no new client shape becomes registrable.
+- PKCE stays required at `/oauth2/authorize` for every one of these clients, and every token still needs the user's sign-in and consent.
+
+The Setup form's own OAuth application door (`/sys-oauth-application/register`) is not affected.
@@ -0,0 +1,345 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * MCP OAuth: anonymous Dynamic Client Registration (RFC 7591) by a client that
+ * sends NO `application_type` (#25118, ruling 6329352251, A1). Every reading
+ * is taken from the REAL `@better-auth/oauth-provider`, booted from the exact
+ * options AuthManager hands it, never from that options object.
+ *
+ * ## Why this file exists
+ *
+ * Local MCP clients (Claude Code, Cursor, VS Code, Codex CLI) register with a
+ * loopback `http` or a custom-scheme redirect and omit `application_type`. The
+ * provider's default filled the missing type with `web` and refused both
+ * redirect forms, so the client failed before its browser opened.
+ * `auth-manager.mcp-oauth-resource.test.ts` registers with an explicit
+ * `application_type: 'native'`, which is why it stayed green through that
+ * defect. Every body below omits the field the way those clients do, and the
+ * first cell sends the card's own request body byte for byte.
+ *
+ * ## The boundary as measured, not as it reads
+ *
+ * 1. A public client with a loopback (`localhost`, `127.0.0.1`) or a
+ *    custom-scheme redirect registers as `native`.
+ * 2. `https://evil.example/cb` alone stays `web`; `http://evil.example/cb` and
+ *    `http://localhost.evil.example` stay refused; an explicit `web` with a
+ *    loopback redirect stays refused (a sent type is never overridden).
+ * 3. The provider classifies by redirect URIs and never reads
+ *    `token_endpoint_auth_method`. So this is NOT "public clients only": a
+ *    CONFIDENTIAL registration with a loopback or custom-scheme redirect and no
+ *    type registers as `native` and is issued a `client_secret`. The same body
+ *    with `application_type: 'native'` spelled out was already accepted.
+ *    "Any redirect qualifies" also lets an https redirect ride beside a
+ *    loopback one in the same body.
+ * 4. For EVERY client registered here, /oauth2/authorize without PKCE is
+ *    refused, and the same request with S256 PKCE reaches consent. The pair
+ *    differs only in the PKCE parameters, so the refusal cannot have another
+ *    cause.
+ * 5. With DCR off the option opens nothing: the card's body is refused.
+ */
+
+import { describe, it, expect, vi, beforeAll } from 'vitest';
+
+import { AuthManager } from './auth-manager';
+import { buildJwtPluginSchema } from './auth-schema-config.js';
+
+// Same pattern as auth-manager.mcp-oauth-resource.test.ts: better-auth is
+// mocked so AuthManager's own instance build stays cheap, and the options it
+// hands `oauthProvider()` are captured. The server every assertion runs
+// against is a SEPARATE, REAL one booted from those options.
+vi.mock('better-auth', () => ({
+  betterAuth: vi.fn(() => ({ handler: vi.fn(), api: {} })),
+}));
+vi.mock('@better-auth/oauth-provider', () => ({
+  oauthProvider: vi.fn((opts: any) => ({ id: 'oauth-provider', _opts: opts })),
+}));
+
+import { oauthProvider } from '@better-auth/oauth-provider';
+
+const BASE_URL = 'https://acme.example.com';
+const AUTH_BASE_PATH = '/api/v1/auth';
+const ISSUER = `${BASE_URL}${AUTH_BASE_PATH}`;
+const MCP_RESOURCE = `${BASE_URL}/api/v1/mcp`;
+// RFC 7636 Appendix B challenge.
+const PKCE_CHALLENGE = 'E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM';
+
+const LOOPBACK = 'http://localhost:63678/callback';
+const LOOPBACK_IPV4 = 'http://127.0.0.1:5000/callback';
+const CUSTOM_SCHEME = 'cursor://anysphere.cursor-retrieval/oauth/callback';
+const HTTPS_FOREIGN = 'https://evil.example/cb';
+const HTTP_FOREIGN = 'http://evil.example/cb';
+const LOOPBACK_LOOKALIKE = 'http://localhost.evil.example/cb';
+
+/**
+ * The card's reproduction body, verbatim: a public client, a loopback `http`
+ * redirect, and no `application_type`.
+ */
+const CARD_BODY = {
+  client_name: 'probe',
+  redirect_uris: [LOOPBACK],
+  grant_types: ['authorization_code', 'refresh_token'],
+  response_types: ['code'],
+  token_endpoint_auth_method: 'none',
+};
+
+/** The card's body with other redirects and/or another auth method. */
+function cardBodyWith(overrides: Record<string, unknown>, dropAuthMethod = false): Record<string, unknown> {
+  const body: Record<string, unknown> = { ...CARD_BODY, ...overrides };
+  if (dropAuthMethod) delete body.token_endpoint_auth_method;
+  return body;
+}
+
+const ENV_KEYS = ['OS_MCP_SERVER_ENABLED', 'OS_OIDC_PROVIDER_ENABLED', 'OS_OIDC_DCR_ENABLED'] as const;
+
+/**
+ * The options AuthManager actually hands `oauthProvider()`, under `env`.
+ * The process env is restored before this returns.
+ */
+async function captureProviderOptions(env: Partial<Record<(typeof ENV_KEYS)[number], string>>): Promise<any> {
+  const saved: Record<string, string | undefined> = {};
+  for (const k of ENV_KEYS) {
+    saved[k] = process.env[k];
+    delete process.env[k];
+  }
+  Object.assign(process.env, env);
+  const warnSpy = vi.spyOn(console, 'warn').mockImplementation(() => {});
+  try {
+    const manager = new AuthManager({ secret: 'test-secret-at-least-32-chars-long', baseUrl: BASE_URL });
+    await manager.getAuthInstance();
+  } finally {
+    warnSpy.mockRestore();
+    for (const k of ENV_KEYS) {
+      if (saved[k] === undefined) delete process.env[k];
+      else process.env[k] = saved[k];
+    }
+  }
+  const opts = (oauthProvider as any).mock.calls.at(-1)?.[0];
+  expect(opts, 'AuthManager must register the oauthProvider plugin').toBeDefined();
+  return opts;
+}
+
+/**
+ * Boots a REAL better-auth server carrying the REAL provider configured with
+ * `opts`, on the in-memory adapter. The table list is derived from the
+ * plugin's own resolved schema, and `jwt()` gets the platform's schema; both
+ * reasons are recorded in auth-manager.mcp-oauth-resource.test.ts.
+ */
+async function bootRealAuthorizationServer(opts: any): Promise<{ auth: any; clientCount: () => number }> {
+  const [{ betterAuth }, { memoryAdapter }, { jwt }, { oauthProvider: realOauthProvider }] = await Promise.all([
+    vi.importActual<typeof import('better-auth')>('better-auth'),
+    import('better-auth/adapters/memory'),
+    import('better-auth/plugins'),
+    vi.importActual<typeof import('@better-auth/oauth-provider')>('@better-auth/oauth-provider'),
+  ]);
+  const plugin = realOauthProvider(opts);
+  const pluginSchema = (plugin as any).schema as Record<string, { modelName?: string }>;
+  const db: Record<string, any[]> = {};
+  for (const m of ['user', 'session', 'account', 'verification', 'jwks']) db[m] = [];
+  for (const [model, def] of Object.entries(pluginSchema ?? {})) db[def.modelName ?? model] = [];
+  const jwtPlugin = jwt({ schema: buildJwtPluginSchema() as any });
+  const jwksModel = (jwtPlugin as any).schema?.jwks?.modelName ?? 'jwks';
+  db[jwksModel] = db[jwksModel] ?? [];
+  const auth = betterAuth({
+    baseURL: BASE_URL,
+    basePath: AUTH_BASE_PATH,
+    secret: 'test-secret-at-least-32-chars-long',
+    database: memoryAdapter(db),
+    emailAndPassword: { enabled: true },
+    plugins: [jwtPlugin, plugin as any],
+  });
+  await auth.$context;
+  const clientModel = pluginSchema?.oauthClient?.modelName ?? 'oauthClient';
+  return { auth, clientCount: () => db[clientModel]?.length ?? 0 };
+}
+
+async function register(auth: any, body: Record<string, unknown>): Promise<{ status: number; body: any }> {
+  const res = await auth.handler(
+    new Request(`${ISSUER}/oauth2/register`, {
+      method: 'POST',
+      headers: { 'content-type': 'application/json' },
+      body: JSON.stringify(body),
+    }),
+  );
+  return { status: res.status, body: (await res.json().catch(() => null)) as any };
+}
+
+async function signUp(auth: any): Promise<string> {
+  const res = await auth.handler(
+    new Request(`${ISSUER}/sign-up/email`, {
+      method: 'POST',
+      headers: { 'content-type': 'application/json' },
+      body: JSON.stringify({ email: 'dev@acme.example.com', password: 'password-12345', name: 'Dev' }),
+    }),
+  );
+  return String(res.headers.get('set-cookie') ?? '')
+    .split(',')
+    .map((c: string) => c.split(';')[0]!.trim())
+    .join('; ');
+}
+
+/** GET /oauth2/authorize for `clientId`, with or without S256 PKCE. */
+async function authorize(
+  auth: any,
+  cookie: string,
+  clientId: string,
+  redirectUri: string,
+  pkce: boolean,
+): Promise<{ status: number; location: string }> {
+  const url = new URL(`${ISSUER}/oauth2/authorize`);
+  url.searchParams.set('client_id', clientId);
+  url.searchParams.set('redirect_uri', redirectUri);
+  url.searchParams.set('response_type', 'code');
+  url.searchParams.set('scope', 'openid profile email data:read');
+  url.searchParams.set('state', 'st');
+  url.searchParams.set('resource', MCP_RESOURCE);
+  if (pkce) {
+    url.searchParams.set('code_challenge', PKCE_CHALLENGE);
+    url.searchParams.set('code_challenge_method', 'S256');
+  }
+  const res = await auth.handler(new Request(url.toString(), { method: 'GET', headers: { cookie } }));
+  return { status: res.status, location: res.headers.get('location') ?? '' };
+}
+
+describe("DCR of a client that omits application_type, on the real provider (#25118, 'infer')", () => {
+  let server: { auth: any; clientCount: () => number };
+  let cookie: string;
+
+  beforeAll(async () => {
+    // MCP on ⇒ the OAuth provider is wired and DCR follows it (resolveDcrEnabled).
+    const opts = await captureProviderOptions({ OS_MCP_SERVER_ENABLED: 'true' });
+    server = await bootRealAuthorizationServer(opts);
+    cookie = await signUp(server.auth);
+  });
+
+  /**
+   * The registration is accepted with `applicationType`, and the authorize
+   * step refuses it without PKCE while the same request with PKCE reaches
+   * consent.
+   */
+  async function expectRegisteredAndPkceBound(
+    body: Record<string, unknown>,
+    expected: { applicationType: 'native' | 'web'; authMethod: string; secret: boolean },
+  ): Promise<void> {
+    const reg = await register(server.auth, body);
+    expect(reg.status, JSON.stringify(reg.body)).toBe(201);
+    expect(reg.body.client_id, 'a registered client has an id').toBeTruthy();
+    expect(reg.body.application_type).toBe(expected.applicationType);
+    expect(reg.body.token_endpoint_auth_method).toBe(expected.authMethod);
+    expect(typeof reg.body.client_secret === 'string', 'whether a client_secret is issued').toBe(expected.secret);
+
+    const redirectUri = (body.redirect_uris as string[])[0]!;
+
+    const withoutPkce = await authorize(server.auth, cookie, reg.body.client_id, redirectUri, false);
+    expect(withoutPkce.location, 'the refusal goes back to the client, never to consent').not.toContain('/oauth/consent');
+    expect(withoutPkce.location.startsWith(redirectUri), withoutPkce.location).toBe(true);
+    const refusal = new URL(withoutPkce.location);
+    expect(refusal.searchParams.get('error'), withoutPkce.location).toBe('invalid_request');
+    expect(refusal.searchParams.get('error_description') ?? '', 'the refusal names PKCE').toMatch(/pkce/i);
+    expect(refusal.searchParams.get('code'), 'no authorization code without PKCE').toBeNull();
+
+    // Differential: the same client, session, redirect and scopes, plus PKCE.
+    const withPkce = await authorize(server.auth, cookie, reg.body.client_id, redirectUri, true);
+    expect(withPkce.location, 'with PKCE the same request reaches consent').toContain('/oauth/consent');
+    expect(withPkce.location).not.toContain('error=');
+  }
+
+  async function expectRefusedRedirect(body: Record<string, unknown>): Promise<void> {
+    const before = server.clientCount();
+    const reg = await register(server.auth, body);
+    expect(reg.status, JSON.stringify(reg.body)).toBe(400);
+    expect(reg.body?.error, JSON.stringify(reg.body)).toBe('invalid_redirect_uri');
+    expect(reg.body?.client_id, 'a refused registration has no client id').toBeUndefined();
+    expect(server.clientCount(), 'a refused registration stores no client').toBe(before);
+  }
+
+  describe('accepted as native: the shapes native MCP clients send', () => {
+    it("the card's own body (public client, loopback http redirect) registers as native", async () => {
+      expect(Object.keys(CARD_BODY), 'the card body omits application_type, as MCP clients do').not.toContain(
+        'application_type',
+      );
+      await expectRegisteredAndPkceBound(CARD_BODY, { applicationType: 'native', authMethod: 'none', secret: false });
+    });
+
+    it('a public client with an http://127.0.0.1 redirect registers as native', async () => {
+      await expectRegisteredAndPkceBound(cardBodyWith({ redirect_uris: [LOOPBACK_IPV4] }), {
+        applicationType: 'native',
+        authMethod: 'none',
+        secret: false,
+      });
+    });
+
+    it('a public client with a custom-scheme redirect registers as native', async () => {
+      await expectRegisteredAndPkceBound(cardBodyWith({ redirect_uris: [CUSTOM_SCHEME] }), {
+        applicationType: 'native',
+        authMethod: 'none',
+        secret: false,
+      });
+    });
+  });
+
+  describe('unchanged: what a web client may and may not register', () => {
+    it('https://evil.example/cb alone stays web', async () => {
+      await expectRegisteredAndPkceBound(cardBodyWith({ redirect_uris: [HTTPS_FOREIGN] }), {
+        applicationType: 'web',
+        authMethod: 'none',
+        secret: false,
+      });
+    });
+
+    it('http://evil.example/cb stays refused', async () => {
+      await expectRefusedRedirect(cardBodyWith({ redirect_uris: [HTTP_FOREIGN] }));
+    });
+
+    it('http://localhost.evil.example stays refused (the loopback match is exact)', async () => {
+      await expectRefusedRedirect(cardBodyWith({ redirect_uris: [LOOPBACK_LOOKALIKE] }));
+    });
+
+    it('an explicit application_type web with a loopback redirect stays refused (a sent type is never overridden)', async () => {
+      await expectRefusedRedirect(cardBodyWith({ application_type: 'web' }));
+    });
+  });
+
+  describe('NOT "public clients only": the classifier reads redirect URIs, never the auth method', () => {
+    it('a confidential client (client_secret_basic) with a loopback redirect registers as native and is issued a client_secret', async () => {
+      await expectRegisteredAndPkceBound(cardBodyWith({ token_endpoint_auth_method: 'client_secret_basic' }), {
+        applicationType: 'native',
+        authMethod: 'client_secret_basic',
+        secret: true,
+      });
+    });
+
+    it('a body that omits the auth method (filled as client_secret_basic) with a loopback redirect registers as native and is issued a client_secret', async () => {
+      await expectRegisteredAndPkceBound(cardBodyWith({}, true), {
+        applicationType: 'native',
+        authMethod: 'client_secret_basic',
+        secret: true,
+      });
+    });
+
+    it('a confidential client with a custom-scheme redirect registers as native and is issued a client_secret', async () => {
+      await expectRegisteredAndPkceBound(
+        cardBodyWith({ token_endpoint_auth_method: 'client_secret_basic', redirect_uris: [CUSTOM_SCHEME] }),
+        { applicationType: 'native', authMethod: 'client_secret_basic', secret: true },
+      );
+    });
+
+    it('ANY qualifying redirect classifies the body: a loopback plus https://evil.example/cb registers as native', async () => {
+      await expectRegisteredAndPkceBound(cardBodyWith({ redirect_uris: [LOOPBACK, HTTPS_FOREIGN] }), {
+        applicationType: 'native',
+        authMethod: 'none',
+        secret: false,
+      });
+    });
+  });
+});
+
+describe("DCR off: 'infer' opens nothing while the registration door is shut", () => {
+  it("refuses the card's own body with access_denied", async () => {
+    const opts = await captureProviderOptions({ OS_MCP_SERVER_ENABLED: 'true', OS_OIDC_DCR_ENABLED: 'false' });
+    const server = await bootRealAuthorizationServer(opts);
+    const reg = await register(server.auth, CARD_BODY);
+    expect(reg.status, JSON.stringify(reg.body)).toBe(403);
+    expect(reg.body?.error, JSON.stringify(reg.body)).toBe('access_denied');
+    expect(server.clientCount(), 'no client is stored').toBe(0);
+  });
+});