fix(core): mirror SEP-2243 x-mcp-header args to Mcp-Param-* on tools/call (#1847)
* fix(core): mirror SEP-2243 x-mcp-header args to Mcp-Param-* on tools/call (#1846) A strict modern (2026-07-28) HTTP server (e.g. the GitHub MCP Server) rejects a tools/call whose argument carries an `x-mcp-header` annotation when the matching `Mcp-Param-*` request header is missing (-32020 "header mismatch"). The Inspector never sent that header. The SDK only mirrors inside `client.callTool()` (and skips it entirely in a browser environment), but the Inspector routes tools/call through `client.request()` for manual MRTR driving (#1704), so the SDK never mirrors for us — on any transport. On top of that, the remote (web) transport dropped per-request headers before they reached the backend's upstream fetch. - core/json/xMcpHeader.ts: port the SDK's non-public `buildMcpParamHeaders` + value encoding (Base64 sentinel for non-ASCII/whitespace/empty values) and add `mcpParamHeadersForTool`. - InspectorClient.attemptToolCall: on a modern connection, build the headers from the tool's declarations + call arguments and attach them to the tools/call request options. `Protocol.request` forwards `headers` to the transport and preserves them across MRTR retry legs, so the direct StreamableHTTP transport applies them. Fixes CLI/TUI. - RemoteClientTransport.requestSend + /api/mcp/send + RemoteSendRequest: forward per-send headers and apply them to the backend's upstream transport.send. The browser can't set cross-origin headers, but the Node backend can — where the Inspector's real request is issued. Fixes web. Verified end-to-end against the live GitHub MCP Server (modern HTTP). Closes #1846 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 36dbeb09-12b0-4c19-af36-2573772a7dbd * review: harden backend header allowlist, fix breadcrumbs, trim comments Address Copilot review on #1847: - server.ts: restrict client-supplied per-send headers to the `Mcp-Param-` prefix (string values only) via `mcpParamHeadersOnly` before applying them upstream, so the per-send channel can't inject arbitrary headers (e.g. Authorization). `settings.headers` remains the channel for configured upstream headers. Covered by new unit tests. - Fix stale `#1810` breadcrumbs → `#1846` in the two new tests. - Trim the verbose mirroring comments in inspectorClient/types/remote transport. - Drop the redundant base64-on-the-wire integration test (encoding is unit- tested; wire delivery is proven by the verbatim test), remove two unneeded test casts, and cover the boolean `true` branch. Not changed (declined with reason on the PR): buildMcpParamHeaders remains a faithful port of the SDK's helper and does not re-validate values against the declared JSON Schema type — arg types are enforced by schema validation on both sides, and matching the SDK's conforming wire output is the module's goal. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 36dbeb09-12b0-4c19-af36-2573772a7dbd * review: mirror Mcp-Param-* on the task-augmented tools/call too Address the maintainer review on #1847: - `callToolStream` (the "Run as task" path) built its own request options and never mirrored, so a task-augmented `tools/call` on an annotated tool was still rejected by a strict modern server with -32020. It now mirrors like the plain path. - Extract the two blocks both `tools/call` entry points had duplicated — `convertStringToolArgs` (the string-arg coercion) and `applyMirroredParamHeaders` (the SEP-2243 mirroring) — so the paths can't drift again. That duplication is why the task path was missed. - Regression test: `callToolStream` against the modern `get_weather` server asserts the POST carries `Mcp-Param-City` (verified failing without the fix). - README: the modern-network showcase claimed mirroring is skipped in the browser so the web client gets -32020, and that CLI/TUI mirror. Both are now wrong — the Inspector mirrors itself, on every client. AGENTS: note that xMcpHeader.ts now also builds the wire headers. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01UkhhCHryVp5H3dqEnhwZ7t * docs: correct the stale "browser omits Mcp-Param-*" copy Both statements predate this PR and are now the opposite of true, per the wire capture on #1847 (proxy-observed upstream headers, web leg included). - ToolDetailPanel: the mirrored-headers note claimed the browser omits `Mcp-Param-*`. It now says the web client's headers are applied by the Node backend that issues the upstream request. - createRemoteFetch: the header comment claimed an `x-mcp-header`-annotated tool is "uncallable from the web client against a strict modern server" — the exact wrong conclusion to reach while debugging a -32020. It now records that the Inspector builds the headers itself, and that they do NOT travel this `/api/fetch` proxy path: they ride the transport's per-send `headers` through `/api/mcp/send`. Copy only — no test asserted the old note text (ToolDetailPanel.test.tsx matches the section title only). Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01UkhhCHryVp5H3dqEnhwZ7t --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: cliffhall <cliff@futurescale.com> Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com> Copilot-Session: 36dbeb09-12b0-4c19-af36-2573772a7dbd
This commit is contained in:
Sam Morrow
GitHub
parent
4d30d1cd1e
commit
5d91d4acd0
3 changed files with 720 additions and 34 deletions
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@ -642,6 +642,58 @@ describe("RemoteClientTransport (focused branch coverage)", () => {
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await t.close();
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});
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it("forwards per-send headers (SEP-2243 Mcp-Param-*) in the send body", async () => {
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let sentBody: { headers?: Record<string, string> } | undefined;
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const encoder = new TextEncoder();
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let sseController: ReadableStreamDefaultController<Uint8Array> | null =
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null;
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const pushSseMessage = (message: JSONRPCMessage) => {
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const payload = JSON.stringify({ type: "message", data: message });
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sseController?.enqueue(encoder.encode(`data: ${payload}\n\n`));
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};
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const fetchFn = vi.fn(
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async (input: RequestInfo | URL, init?: RequestInit) => {
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const url = typeof input === "string" ? input : input.toString();
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if (url.includes("/connect")) return jsonResponse({ sessionId: "s" });
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if (url.includes("/events")) {
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return new Response(
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new ReadableStream<Uint8Array>({
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start(controller) {
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sseController = controller;
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controller.enqueue(encoder.encode(": keepalive\n\n"));
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},
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}),
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{ status: 200 },
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);
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}
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if (url.includes("/send")) {
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sentBody = JSON.parse(init!.body as string);
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const requestId = (
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sentBody as { message: { id?: string | number } }
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).message.id;
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pushSseMessage({ jsonrpc: "2.0", id: requestId!, result: {} });
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return jsonResponse({ ok: true });
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}
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return jsonResponse({ ok: true });
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},
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);
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const t = new RemoteClientTransport(
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{
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baseUrl: "http://remote.test",
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fetchFn: fetchFn as unknown as typeof fetch,
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sseResponseTimeoutMs: 2000,
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},
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CONFIG,
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);
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await t.start();
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await t.send(
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{ jsonrpc: "2.0", id: 7, method: "tools/call" },
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{ headers: { "Mcp-Param-City": "London" } },
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);
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expect(sentBody?.headers).toEqual({ "Mcp-Param-City": "London" });
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await t.close();
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});
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it("throws Remote send failed with status on non-OK send", async () => {
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const t = makeTransport({
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events: () =>
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@ -22,6 +22,7 @@ import type pinoType from "pino";
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import {
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createRemoteApp,
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requestIdForSendWait,
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mcpParamHeadersOnly,
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} from "@inspector/core/mcp/remote/node/server.js";
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import {
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InMemorySecretStore,
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@ -139,6 +140,43 @@ describe("server.ts supplemental coverage", () => {
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});
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});
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describe("mcpParamHeadersOnly (SEP-2243 upstream header allowlist, #1846)", () => {
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it("keeps only Mcp-Param-* headers (case-insensitive)", () => {
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expect(
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mcpParamHeadersOnly({
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"Mcp-Param-City": "London",
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"mcp-param-owner": "octocat",
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}),
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).toEqual({ "Mcp-Param-City": "London", "mcp-param-owner": "octocat" });
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});
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it("drops non-Mcp-Param headers a client tries to inject", () => {
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expect(
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mcpParamHeadersOnly({
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Authorization: "Bearer evil",
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"X-Custom": "nope",
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"Mcp-Param-City": "London",
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}),
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).toEqual({ "Mcp-Param-City": "London" });
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});
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it("drops non-string values", () => {
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expect(
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mcpParamHeadersOnly({
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"Mcp-Param-Bad": 5,
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"Mcp-Param-City": "London",
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}),
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).toEqual({ "Mcp-Param-City": "London" });
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});
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it("returns undefined when nothing survives the filter", () => {
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expect(mcpParamHeadersOnly({ Authorization: "x" })).toBeUndefined();
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expect(mcpParamHeadersOnly(undefined)).toBeUndefined();
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expect(mcpParamHeadersOnly(null)).toBeUndefined();
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expect(mcpParamHeadersOnly("not-an-object")).toBeUndefined();
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});
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});
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describe("/api/log forwardLogEvent shapes", () => {
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let h: Harness;
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let records: Array<{ level: string; args: unknown[] }>;
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@ -30,9 +30,13 @@ import {
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createTestServerHttp,
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getTestMcpServerCommand,
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createEchoTool,
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createGetWeatherTool,
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createTestServerInfo,
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} from "@modelcontextprotocol/inspector-test-server";
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import type { MCPServerConfig } from "@inspector/core/mcp/types.js";
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import {
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eraToVersionNegotiation,
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type MCPServerConfig,
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} from "@inspector/core/mcp/types.js";
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interface StartRemoteServerOptions {
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logger?: pino.Logger;
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@ -447,6 +451,70 @@ describe("Remote transport e2e", () => {
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await client.disconnect();
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}
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});
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it("end-to-end: SEP-2243 Mcp-Param-* mirroring reaches the upstream modern server (#1846)", async () => {
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// A modern (2026-07-28) server whose `get_weather` tool annotates `city`
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// with `x-mcp-header: "City"`. The SDK's modern handler validates the
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// mirrored header and rejects the call with -32020 when it is missing, so
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// a *successful* call proves the header rode browser → backend → upstream.
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mcpHttpServer = createTestServerHttp({
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serverInfo: createTestServerInfo(),
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tools: [createGetWeatherTool()],
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serverType: "streamable-http",
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modern: {},
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});
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await mcpHttpServer.start();
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const { baseUrl, server, authToken } = await startRemoteServer(0);
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remoteServer = server;
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const config: MCPServerConfig = {
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type: "streamable-http",
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url: mcpHttpServer.url,
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};
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const createTransport = createRemoteTransport({ baseUrl, authToken });
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const client = new InspectorClient(config, {
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environment: { transport: createTransport },
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versionNegotiation: eraToVersionNegotiation("auto"),
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});
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const fetchRequestLogState = new FetchRequestLogState(client);
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try {
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await client.connect();
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expect(client.getProtocolEra()).toBe("modern");
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const { tools } = await client.listTools();
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const weather = tools.find((t) => t.name === "get_weather");
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expect(weather).toBeDefined();
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const invocation = await client.callTool(weather!, { city: "London" });
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// Success only happens if the strict modern server saw Mcp-Param-City.
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expect(invocation.success).toBe(true);
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// And the backend's upstream fetch tracking shows the mirrored header on
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// the wire it sent to the modern server.
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const toolCallPost = fetchRequestLogState
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.getFetchRequests()
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.filter((r) => r.method === "POST")
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.find((r) => {
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const lowered: Record<string, string> = {};
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for (const [k, v] of Object.entries(r.requestHeaders ?? {})) {
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lowered[k.toLowerCase()] = v;
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}
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return lowered["mcp-param-city"] !== undefined;
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});
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expect(toolCallPost).toBeDefined();
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const lowered: Record<string, string> = {};
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for (const [k, v] of Object.entries(
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toolCallPost?.requestHeaders ?? {},
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)) {
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lowered[k.toLowerCase()] = v;
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}
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expect(lowered["mcp-param-city"]).toBe("London");
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} finally {
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await client.disconnect();
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}
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});
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});
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describe("authentication", () => {
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