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feat(web): honor _meta.ui.domain with a dedicated app origin

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An MCP App is rendered by handing its HTML to the sandbox proxy as
`srcdoc`, in a frame sandboxed without `allow-same-origin` — the #1565
isolation model. That gives the app document an opaque origin, so every
request it makes carries `Origin: null` and no CORS / OAuth-callback /
API-key allowlist can admit it. `_meta.ui.domain` is the spec field a
server uses to ask its host for a stable, dedicated origin, and it was
being dropped on the floor.

The field is explicitly host-dependent and the Inspector owns no domain
infrastructure, so it treats any non-empty value as a request rather than
an address, and answers with a real loopback origin on its own listener
(MCP_APP_ORIGIN_PORT, default 6276). One shared origin, path-keyed per
document: that delivers what the field is for without minting a port or
DNS name per app, and is therefore not a per-app isolation boundary.

The inner frame is granted `allow-same-origin` on this path only, which
is what makes the origin real. It is not a #1565 regression: the listener
is on its own port, so the app stays cross-origin to both the proxy and
the Inspector. The proxy refuses the grant if the URL's origin equals its
own, and the grant is never reachable from the server-supplied `sandbox`
string, which is still stripped. The per-app CSP is delivered as a real
response header there rather than only as a <meta>.

Every failure path falls back to the default srcdoc render with a console
warning naming the field, rather than blanking the app.

Also fixes a pre-existing `tsc -b` break on v2/main (useServers.test.tsx
passed `metadata: []` where `RequestMetadata` is expected), which has had
CI red since #2087 and blocks the pre-push gate.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0177mPHAdECD18nLLCTwR5rh
Signed-off-by: cliffhall <cliff@futurescale.com>
This commit is contained in:
cliffhall 2026-08-23 23:03:55 -04:00 • committed by GitHub
commit ec40cf5531
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1 changed files with 1554 additions and 18 deletions
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10
clients/web/server/web-server-config.ts
View file

@ -19,6 +19,7 @@ import type { SecretStorageInfo } from "../../../core/auth/secret-storage-info.t
import { secretStorageSummary } from "../../../core/auth/secret-storage-info.ts";
import { readInspectorVersionSafe } from "../../../core/node/version.ts";
import { resolveSandboxPort } from "./sandbox-controller.js";
import { resolveAppOriginPort } from "./app-origin-controller.js";
import { resolveBindHostname } from "./resolve-bind-host.js";
import {
canonicalUrlHost,
@ -66,6 +67,13 @@ export interface WebServerConfig {
/** Sandbox port (0 = dynamic). */
sandboxPort: number;
sandboxHost: string;
/**
* Port for the dedicated app origin (#2056) — the listener that serves an
* MCP App declaring `_meta.ui.domain` so its requests carry a real `Origin`
* instead of `null`. `0` = dynamic. Bound on {@link sandboxHost}, the same
* address the sandbox uses.
*/
appOriginPort: number;
logger: Logger | undefined;
/** When true, open browser after server starts. */
autoOpen: boolean;
@ -369,6 +377,7 @@ export function buildWebServerConfig(
"");
const sandboxPort = resolveSandboxPort();
const appOriginPort = resolveAppOriginPort();
let logger: Logger | undefined;
if (process.env.MCP_LOG_FILE) {
@ -439,6 +448,7 @@ export function buildWebServerConfig(
: defaultAllowedOrigins(hostname, port),
sandboxPort,
sandboxHost: hostname,
appOriginPort,
logger,
autoOpen: resolveAutoOpen(),
};