fix(mcp): scope OAuth resource headers

packages/opencode/src/cli/cmd/mcp.ts

@@ -769,7 +769,10 @@ export const McpDebugCommand = effectCmd({
           prompts.log.info(`WWW-Authenticate: ${wwwAuth}`)
         }
 
-        if (response.status === 401) {
+        if (
+          response.status === 401 &&
+          !Object.keys(serverConfig.headers ?? {}).some((key) => key.toLowerCase() === "authorization")
+        ) {
           prompts.log.warn("Server returned 401 Unauthorized")
 
           // Try to discover OAuth metadata

packages/opencode/src/mcp/index.ts

@@ -226,7 +226,8 @@ export const layer = Layer.effect(
       key: string,
       mcp: ConfigMCPV1.Info & { type: "remote" },
     ) {
-      const oauthDisabled = mcp.oauth === false
+      const oauthDisabled =
+        mcp.oauth === false || Object.keys(mcp.headers ?? {}).some((key) => key.toLowerCase() === "authorization")
       const oauthConfig = typeof mcp.oauth === "object" ? mcp.oauth : undefined
       const url = remoteURL(mcp.url)
       if (!url) {
@@ -797,6 +798,8 @@ export const layer = Layer.effect(
       const mcpConfig = yield* requireMcpConfig(mcpName)
       if (mcpConfig.type !== "remote") throw new Error(`MCP server ${mcpName} is not a remote server`)
       if (mcpConfig.oauth === false) throw new Error(`MCP server ${mcpName} has OAuth explicitly disabled`)
+      if (Object.keys(mcpConfig.headers ?? {}).some((key) => key.toLowerCase() === "authorization"))
+        throw new Error(`MCP server ${mcpName} uses static Authorization`)
       const url = remoteURL(mcpConfig.url)
       if (!url) throw new Error(`Invalid MCP URL for "${mcpName}"`)
 

packages/opencode/test/mcp/headers.test.ts

@@ -49,7 +49,7 @@ const { MCP } = await import("../../src/mcp/index")
 const it = testEffect(MCP.defaultLayer)
 
 describe("mcp.headers", () => {
-  it.instance("headers are passed to transports when oauth is enabled (default)", () =>
+  it.instance("static authorization is passed to transports without oauth", () =>
     Effect.gen(function* () {
       const mcp = yield* MCP.Service
       yield* mcp
@@ -72,8 +72,8 @@ describe("mcp.headers", () => {
           Authorization: "Bearer test-token",
           "X-Custom-Header": "custom-value",
         })
-        // OAuth should be enabled by default, so authProvider should exist
+        // Static Authorization and OAuth are mutually exclusive.
-        expect(call.options.authProvider).toBeDefined()
+        expect(call.options.authProvider).toBeUndefined()
       }
     }),
   )
@@ -105,6 +105,28 @@ describe("mcp.headers", () => {
     }),
   )
 
+  it.instance("case-insensitive authorization disables oauth", () =>
+    Effect.gen(function* () {
+      const mcp = yield* MCP.Service
+      yield* mcp
+        .add("test-server-lowercase-auth", {
+          type: "remote",
+          url: "https://example.com/mcp",
+          headers: { authorization: "Bearer test-token", "X-Custom-Header": "custom-value" },
+        })
+        .pipe(Effect.catch(() => Effect.void))
+
+      expect(transportCalls.length).toBeGreaterThanOrEqual(1)
+      for (const call of transportCalls) {
+        expect(call.options.requestInit?.headers).toEqual({
+          authorization: "Bearer test-token",
+          "X-Custom-Header": "custom-value",
+        })
+        expect(call.options.authProvider).toBeUndefined()
+      }
+    }),
+  )
+
   it.instance("no requestInit when headers are not provided", () =>
     Effect.gen(function* () {
       const mcp = yield* MCP.Service

packages/opencode/test/mcp/oauth-header-isolation.test.ts

@@ -0,0 +1,284 @@
+import { describe, expect, test } from "bun:test"
+import type { OAuthClientProvider } from "@modelcontextprotocol/sdk/client/auth.js"
+import type {
+  OAuthClientInformationMixed,
+  OAuthClientMetadata,
+  OAuthTokens,
+} from "@modelcontextprotocol/sdk/shared/auth.js"
+// @ts-expect-error Bun's query cache key avoids process-global module mocks from other test files.
+import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js?oauth-header-isolation"
+
+const canary = "resource-secret"
+const staticAuthorization = "Bearer static-resource-token"
+const basicAuthorization = `Basic ${btoa("client:secret")}`
+
+describe("MCP OAuth header isolation", () => {
+  test("keeps resource headers on same-origin protected resource metadata", async () => {
+    using authorizationServer = serve(() =>
+      Response.json({
+        issuer: authorizationServer.origin,
+        authorization_endpoint: `${authorizationServer.origin}/authorize`,
+        token_endpoint: `${authorizationServer.origin}/token`,
+        response_types_supported: ["code"],
+        code_challenge_methods_supported: ["S256"],
+      }),
+    )
+    using resource = serve((request) => {
+      if (new URL(request.url).pathname === "/prm") {
+        return Response.json({
+          resource: `${resource.origin}/mcp`,
+          authorization_servers: [authorizationServer.origin],
+        })
+      }
+      return new Response(null, {
+        status: 401,
+        headers: { "WWW-Authenticate": `Bearer resource_metadata="${resource.origin}/prm"` },
+      })
+    })
+    const transport = new StreamableHTTPClientTransport(new URL(`${resource.origin}/mcp`), {
+      authProvider: createProvider({
+        clientInformation: { client_id: "client", token_endpoint_auth_method: "none" },
+      }),
+      requestInit: { headers: { "X-Resource-Canary": canary, Authorization: staticAuthorization } },
+    })
+
+    await transport.start()
+    await expect(transport.send(request())).rejects.toThrow("Unauthorized")
+    await transport.close()
+
+    expect(resource.requests.map((request) => new URL(request.url).pathname)).toEqual(["/mcp", "/prm"])
+    expectResourceHeaders(resource.requests)
+    expectNoResourceHeaders(authorizationServer.requests)
+  })
+
+  test("does not follow protected resource metadata redirects with resource headers", async () => {
+    using target = serve(() => Response.json({}))
+    using resource = serve((request) => {
+      if (new URL(request.url).pathname === "/prm") {
+        return Response.redirect(`${target.origin}/prm`)
+      }
+      return new Response(null, {
+        status: 401,
+        headers: { "WWW-Authenticate": `Bearer resource_metadata="${resource.origin}/prm"` },
+      })
+    })
+    const transport = new StreamableHTTPClientTransport(new URL(`${resource.origin}/mcp`), {
+      authProvider: createProvider({
+        clientInformation: { client_id: "client", token_endpoint_auth_method: "none" },
+      }),
+      requestInit: { headers: { "X-Resource-Canary": canary } },
+    })
+
+    await transport.start()
+    await expect(transport.send(request())).rejects.toThrow("Unauthorized")
+    await transport.close()
+
+    expect(target.requests).toHaveLength(0)
+  })
+
+  test("keeps resource headers out of discovery, registration, and token exchange", async () => {
+    using token = serve(() => Response.json({ access_token: "access", token_type: "Bearer", refresh_token: "refresh" }))
+    using registration = serve(() =>
+      Response.json({
+        client_id: "client",
+        client_secret: "secret",
+        token_endpoint_auth_method: "client_secret_basic",
+        redirect_uris: ["http://127.0.0.1/callback"],
+        client_name: "OpenCode test",
+        grant_types: ["authorization_code", "refresh_token"],
+        response_types: ["code"],
+      }),
+    )
+    using authorizationServer = serve(() =>
+      Response.json({
+        issuer: authorizationServer.origin,
+        authorization_endpoint: `${authorizationServer.origin}/authorize`,
+        token_endpoint: `${token.origin}/token`,
+        registration_endpoint: `${registration.origin}/register`,
+        response_types_supported: ["code"],
+        code_challenge_methods_supported: ["S256"],
+        token_endpoint_auth_methods_supported: ["client_secret_basic"],
+      }),
+    )
+    using metadata = serve(() =>
+      Response.json({
+        resource: `${resource.origin}/mcp`,
+        authorization_servers: [authorizationServer.origin],
+      }),
+    )
+    using resource = serve(
+      () =>
+        new Response(null, {
+          status: 401,
+          headers: { "WWW-Authenticate": `Bearer resource_metadata="${metadata.origin}/prm"` },
+        }),
+    )
+    const provider = createProvider()
+    const transport = new StreamableHTTPClientTransport(new URL(`${resource.origin}/mcp`), {
+      authProvider: provider,
+      requestInit: { headers: { "X-Resource-Canary": canary, aUtHoRiZaTiOn: staticAuthorization } },
+    })
+
+    await transport.start()
+    await expect(transport.send(request())).rejects.toThrow("Unauthorized")
+    await transport.finishAuth("authorization-code")
+    await transport.close()
+
+    expectResourceHeaders(resource.requests)
+    expectNoResourceHeaders(metadata.requests)
+    expectNoResourceHeaders(authorizationServer.requests)
+    expectNoResourceHeaders(registration.requests)
+    expectNoResourceHeaders(token.requests)
+    expect(registration.requests).toHaveLength(1)
+    expect(token.requests).toHaveLength(1)
+    expectAuthorization(token.requests[0], basicAuthorization)
+    expect(new URLSearchParams(token.requests[0].body).get("grant_type")).toBe("authorization_code")
+  })
+
+  test("keeps resource headers out of token refresh", async () => {
+    using refresh = serve(() => Response.json({ access_token: "fresh-access", token_type: "Bearer" }))
+    using authorizationServer = serve(() =>
+      Response.json({
+        issuer: authorizationServer.origin,
+        authorization_endpoint: `${authorizationServer.origin}/authorize`,
+        token_endpoint: `${refresh.origin}/refresh`,
+        response_types_supported: ["code"],
+        code_challenge_methods_supported: ["S256"],
+        token_endpoint_auth_methods_supported: ["client_secret_basic"],
+      }),
+    )
+    using metadata = serve(() =>
+      Response.json({
+        resource: `${resource.origin}/mcp`,
+        authorization_servers: [authorizationServer.origin],
+      }),
+    )
+    using resource = serve((request) => {
+      if (resource.requests.length === 1) {
+        return new Response(null, {
+          status: 401,
+          headers: { "WWW-Authenticate": `Bearer resource_metadata="${metadata.origin}/prm"` },
+        })
+      }
+      return Response.json({ jsonrpc: "2.0", id: 1, result: {} })
+    })
+    const transport = new StreamableHTTPClientTransport(new URL(`${resource.origin}/mcp`), {
+      authProvider: createProvider({
+        clientInformation: {
+          client_id: "client",
+          client_secret: "secret",
+          token_endpoint_auth_method: "client_secret_basic",
+        },
+        tokens: { access_token: "expired-access", token_type: "Bearer", refresh_token: "refresh-token" },
+      }),
+      requestInit: { headers: { "X-Resource-Canary": canary, authorization: staticAuthorization } },
+    })
+    transport.onmessage = () => {}
+
+    await transport.start()
+    await transport.send(request())
+    await transport.close()
+
+    expect(resource.requests).toHaveLength(2)
+    expectResourceHeaders(resource.requests, ["Bearer expired-access", "Bearer fresh-access"])
+    expectNoResourceHeaders(metadata.requests)
+    expectNoResourceHeaders(authorizationServer.requests)
+    expectNoResourceHeaders(refresh.requests)
+    expect(refresh.requests).toHaveLength(1)
+    expectAuthorization(refresh.requests[0], basicAuthorization)
+    expect(new URLSearchParams(refresh.requests[0].body).get("grant_type")).toBe("refresh_token")
+  })
+})
+
+function createProvider(initial?: {
+  clientInformation?: OAuthClientInformationMixed
+  tokens?: OAuthTokens
+}): OAuthClientProvider {
+  let clientInformation = initial?.clientInformation
+  let tokens = initial?.tokens
+  let codeVerifier = ""
+  return {
+    redirectUrl: "http://127.0.0.1/callback",
+    clientMetadata: {
+      redirect_uris: ["http://127.0.0.1/callback"],
+      client_name: "OpenCode test",
+      grant_types: ["authorization_code", "refresh_token"],
+      response_types: ["code"],
+    } satisfies OAuthClientMetadata,
+    clientInformation: () => clientInformation,
+    saveClientInformation: (value) => {
+      clientInformation = value
+    },
+    tokens: () => tokens,
+    saveTokens: (value) => {
+      tokens = value
+    },
+    redirectToAuthorization: () => {},
+    saveCodeVerifier: (value) => {
+      codeVerifier = value
+    },
+    codeVerifier: () => codeVerifier,
+    state: () => "state",
+  }
+}
+
+function request() {
+  return {
+    jsonrpc: "2.0" as const,
+    id: 1,
+    method: "initialize",
+    params: {
+      protocolVersion: "2025-06-18",
+      capabilities: {},
+      clientInfo: { name: "opencode-test", version: "1" },
+    },
+  }
+}
+
+function expectResourceHeaders(requests: CapturedRequest[], authorization: string | string[] = staticAuthorization) {
+  expect(requests.length).toBeGreaterThan(0)
+  for (const [index, request] of requests.entries()) {
+    expect(request.headers.get("x-resource-canary")).toBe(canary)
+    expectAuthorization(request, Array.isArray(authorization) ? authorization[index] : authorization)
+  }
+}
+
+function expectNoResourceHeaders(requests: CapturedRequest[]) {
+  expect(requests.length).toBeGreaterThan(0)
+  for (const request of requests) {
+    expect(request.headers.get("x-resource-canary")).toBeNull()
+    expect(request.headers.get("authorization")).not.toBe(staticAuthorization)
+  }
+}
+
+function expectAuthorization(request: CapturedRequest, value: string) {
+  expect([...request.headers].filter(([name]) => name === "authorization")).toEqual([["authorization", value]])
+}
+
+interface CapturedRequest {
+  url: string
+  headers: Headers
+  body: string
+}
+
+function serve(handler: (request: CapturedRequest) => Response | Promise<Response>) {
+  const requests: CapturedRequest[] = []
+  const server = Bun.serve({
+    hostname: "127.0.0.1",
+    port: 0,
+    async fetch(request) {
+      const captured = {
+        url: request.url,
+        headers: new Headers(request.headers),
+        body: await request.text(),
+      }
+      requests.push(captured)
+      return handler(captured)
+    },
+  })
+  return {
+    origin: `http://127.0.0.1:${server.port}`,
+    requests,
+    [Symbol.dispose]: () => server.stop(true),
+  }
+}

patches/@modelcontextprotocol%2Fsdk@1.29.0.patch

@@ -1,5 +1,59 @@
+diff --git a/dist/cjs/client/auth.js b/dist/cjs/client/auth.js
+index c2e4fa91d26f5336889f6afa416147db75fc4872..6fe80dd336252838adf47b0a8e022e55d11e3657 100644
+--- a/dist/cjs/client/auth.js
++++ b/dist/cjs/client/auth.js
+@@ -186,7 +186,7 @@ async function auth(provider, options) {
+         throw error;
+     }
+ }
+-async function authInternal(provider, { serverUrl, authorizationCode, scope, resourceMetadataUrl, fetchFn }) {
++async function authInternal(provider, { serverUrl, authorizationCode, scope, resourceMetadataUrl, fetchFn, resourceMetadataFetchFn }) {
+     // Check if the provider has cached discovery state to skip discovery
+     const cachedState = await provider.discoveryState?.();
+     let resourceMetadata;
+@@ -198,6 +198,9 @@ async function authInternal(provider, { serverUrl, authorizationCode, scope, res
+     if (!effectiveResourceMetadataUrl && cachedState?.resourceMetadataUrl) {
+         effectiveResourceMetadataUrl = new URL(cachedState.resourceMetadataUrl);
+     }
++    const protectedResourceFetchFn = !effectiveResourceMetadataUrl || effectiveResourceMetadataUrl.origin === new URL(serverUrl).origin
++        ? (resourceMetadataFetchFn ?? fetchFn)
++        : fetchFn;
+     if (cachedState?.authorizationServerUrl) {
+         // Restore discovery state from cache
+         authorizationServerUrl = cachedState.authorizationServerUrl;
+@@ -207,7 +210,7 @@ async function authInternal(provider, { serverUrl, authorizationCode, scope, res
+         // If resource metadata wasn't cached, try to fetch it for selectResourceURL
+         if (!resourceMetadata) {
+             try {
+-                resourceMetadata = await discoverOAuthProtectedResourceMetadata(serverUrl, { resourceMetadataUrl: effectiveResourceMetadataUrl }, fetchFn);
++                resourceMetadata = await discoverOAuthProtectedResourceMetadata(serverUrl, { resourceMetadataUrl: effectiveResourceMetadataUrl }, protectedResourceFetchFn);
+             }
+             catch {
+                 // RFC 9728 not available — selectResourceURL will handle undefined
+@@ -225,7 +228,11 @@ async function authInternal(provider, { serverUrl, authorizationCode, scope, res
+     }
+     else {
+         // Full discovery via RFC 9728
+-        const serverInfo = await discoverOAuthServerInfo(serverUrl, { resourceMetadataUrl: effectiveResourceMetadataUrl, fetchFn });
++        const serverInfo = await discoverOAuthServerInfo(serverUrl, {
++            resourceMetadataUrl: effectiveResourceMetadataUrl,
++            fetchFn,
++            resourceMetadataFetchFn: protectedResourceFetchFn
++        });
+         authorizationServerUrl = serverInfo.authorizationServerUrl;
+         metadata = serverInfo.authorizationServerMetadata;
+         resourceMetadata = serverInfo.resourceMetadata;
+@@ -688,7 +695,7 @@ async function discoverOAuthServerInfo(serverUrl, opts) {
+     let resourceMetadata;
+     let authorizationServerUrl;
+     try {
+-        resourceMetadata = await discoverOAuthProtectedResourceMetadata(serverUrl, { resourceMetadataUrl: opts?.resourceMetadataUrl }, opts?.fetchFn);
++        resourceMetadata = await discoverOAuthProtectedResourceMetadata(serverUrl, { resourceMetadataUrl: opts?.resourceMetadataUrl }, opts?.resourceMetadataFetchFn ?? opts?.fetchFn);
+         if (resourceMetadata.authorization_servers && resourceMetadata.authorization_servers.length > 0) {
+             authorizationServerUrl = resourceMetadata.authorization_servers[0];
+         }
 diff --git a/dist/cjs/client/index.d.ts b/dist/cjs/client/index.d.ts
-index 1822bf749aec71d2bb295083d832114ee187bb67..58b859a7b32222fb5cb9f2011fdc5d010f3d05fb 100644
+index 6f567a193626587a2730b5a49293ca5dfd4181ea..5b7c841c000508e389ce617f559f7c2a5126ca9f 100644
 --- a/dist/cjs/client/index.d.ts
 +++ b/dist/cjs/client/index.d.ts
 @@ -428,6 +428,8 @@ export declare class Client<RequestT extends Request = Request, NotificationT ex
@@ -7,25 +61,12 @@ index 1822bf749aec71d2bb295083d832114ee187bb67..58b859a7b32222fb5cb9f2011fdc5d01
       * For task-based execution with streaming behavior, use client.experimental.tasks.callToolStream() instead.
       */
 +    callTool(params: CallToolRequest['params'], resultSchema?: undefined, options?: RequestOptions): Promise<SchemaOutput<typeof CallToolResultSchema>>;
-+    callTool<T extends typeof CallToolResultSchema | typeof CompatibilityCallToolResultSchema>(params: CallToolRequest['params'], resultSchema: T, options?: RequestOptions): Promise<SchemaOutput<T>>;
-     callTool(params: CallToolRequest['params'], resultSchema?: typeof CallToolResultSchema | typeof CompatibilityCallToolResultSchema, options?: RequestOptions): Promise<{
-         [x: string]: unknown;
-         content: ({
-diff --git a/dist/esm/client/index.d.ts b/dist/esm/client/index.d.ts
-index 1822bf749aec71d2bb295083d832114ee187bb67..58b859a7b32222fb5cb9f2011fdc5d010f3d05fb 100644
---- a/dist/esm/client/index.d.ts
-+++ b/dist/esm/client/index.d.ts
-@@ -428,6 +428,8 @@ export declare class Client<RequestT extends Request = Request, NotificationT ex
-      *
-      * For task-based execution with streaming behavior, use client.experimental.tasks.callToolStream() instead.
-      */
-+    callTool(params: CallToolRequest['params'], resultSchema?: undefined, options?: RequestOptions): Promise<SchemaOutput<typeof CallToolResultSchema>>;
 +    callTool<T extends typeof CallToolResultSchema | typeof CompatibilityCallToolResultSchema>(params: CallToolRequest['params'], resultSchema: T, options?: RequestOptions): Promise<SchemaOutput<T>>;
      callTool(params: CallToolRequest['params'], resultSchema?: typeof CallToolResultSchema | typeof CompatibilityCallToolResultSchema, options?: RequestOptions): Promise<{
          [x: string]: unknown;
          content: ({
 diff --git a/dist/cjs/client/index.js b/dist/cjs/client/index.js
-index 6ac1da14dc7f6211ae70f7711c124b76098816d8..adb5b7bd45514a406a0f7e40b64631c101584c84 100644
+index 6ac1da14dc7f6211ae70f7711c124b76098816d8..88e58b90b673cb0f9c60920edec7d2ebb16f112b 100644
 --- a/dist/cjs/client/index.js
 +++ b/dist/cjs/client/index.js
 @@ -288,41 +288,16 @@ class Client extends protocol_js_1.Protocol {
@@ -112,11 +153,119 @@ index 6ac1da14dc7f6211ae70f7711c124b76098816d8..adb5b7bd45514a406a0f7e40b64631c1
      /**
       * After initialization has completed, this will be populated with the server's reported capabilities.
       */
+diff --git a/dist/cjs/client/sse.js b/dist/cjs/client/sse.js
+index 8ca8dad652e76c299927f836cf622c0be877e1d4..14cc1b969ac51ecb6f894608f079f4f04d8acd62 100644
+--- a/dist/cjs/client/sse.js
++++ b/dist/cjs/client/sse.js
+@@ -27,7 +27,9 @@ class SSEClientTransport {
+         this._requestInit = opts?.requestInit;
+         this._authProvider = opts?.authProvider;
+         this._fetch = opts?.fetch;
+-        this._fetchWithInit = (0, transport_js_1.createFetchWithInit)(opts?.fetch, opts?.requestInit);
++        this._resourceFetchWithInit = (0, transport_js_1.createFetchWithInit)(opts?.fetch, { ...opts?.requestInit, redirect: 'error' });
++        const oauthRequestInit = opts?.requestInit ? { ...opts.requestInit, headers: undefined } : undefined;
++        this._fetchWithInit = (0, transport_js_1.createFetchWithInit)(opts?.fetch, oauthRequestInit);
+     }
+     async _authThenStart() {
+         if (!this._authProvider) {
+@@ -39,7 +41,8 @@ class SSEClientTransport {
+                 serverUrl: this._url,
+                 resourceMetadataUrl: this._resourceMetadataUrl,
+                 scope: this._scope,
+-                fetchFn: this._fetchWithInit
++                fetchFn: this._fetchWithInit,
++                resourceMetadataFetchFn: this._resourceFetchWithInit
+             });
+         }
+         catch (error) {
+@@ -63,10 +66,11 @@ class SSEClientTransport {
+             headers['mcp-protocol-version'] = this._protocolVersion;
+         }
+         const extraHeaders = (0, transport_js_1.normalizeHeaders)(this._requestInit?.headers);
+-        return new Headers({
+-            ...headers,
+-            ...extraHeaders
+-        });
++        const result = new Headers(extraHeaders);
++        for (const [name, value] of Object.entries(headers)) {
++            result.set(name, value);
++        }
++        return result;
+     }
+     _startOrAuth() {
+         const fetchImpl = (this?._eventSourceInit?.fetch ?? this._fetch ?? fetch);
+@@ -149,7 +153,8 @@ class SSEClientTransport {
+             authorizationCode,
+             resourceMetadataUrl: this._resourceMetadataUrl,
+             scope: this._scope,
+-            fetchFn: this._fetchWithInit
++            fetchFn: this._fetchWithInit,
++            resourceMetadataFetchFn: this._resourceFetchWithInit
+         });
+         if (result !== 'AUTHORIZED') {
+             throw new auth_js_1.UnauthorizedError('Failed to authorize');
+@@ -185,7 +190,8 @@ class SSEClientTransport {
+                         serverUrl: this._url,
+                         resourceMetadataUrl: this._resourceMetadataUrl,
+                         scope: this._scope,
+-                        fetchFn: this._fetchWithInit
++                        fetchFn: this._fetchWithInit,
++                        resourceMetadataFetchFn: this._resourceFetchWithInit
+                     });
+                     if (result !== 'AUTHORIZED') {
+                         throw new auth_js_1.UnauthorizedError();
 diff --git a/dist/cjs/client/streamableHttp.js b/dist/cjs/client/streamableHttp.js
-index a29a7d3a0f14d9cd800ef5b296485237350c666f..c362ae5fe6c62c8c8eae7e2e61de1eedff5443c9 100644
+index a29a7d3a0f14d9cd800ef5b296485237350c666f..54ac759eb19df7c6f16fc031a689270acb5c3922 100644
 --- a/dist/cjs/client/streamableHttp.js
 +++ b/dist/cjs/client/streamableHttp.js
-@@ -290,7 +290,38 @@ class StreamableHTTPClientTransport {
+@@ -33,7 +33,9 @@ class StreamableHTTPClientTransport {
+         this._requestInit = opts?.requestInit;
+         this._authProvider = opts?.authProvider;
+         this._fetch = opts?.fetch;
+-        this._fetchWithInit = (0, transport_js_1.createFetchWithInit)(opts?.fetch, opts?.requestInit);
++        this._resourceFetchWithInit = (0, transport_js_1.createFetchWithInit)(opts?.fetch, { ...opts?.requestInit, redirect: 'error' });
++        const oauthRequestInit = opts?.requestInit ? { ...opts.requestInit, headers: undefined } : undefined;
++        this._fetchWithInit = (0, transport_js_1.createFetchWithInit)(opts?.fetch, oauthRequestInit);
+         this._sessionId = opts?.sessionId;
+         this._reconnectionOptions = opts?.reconnectionOptions ?? DEFAULT_STREAMABLE_HTTP_RECONNECTION_OPTIONS;
+     }
+@@ -47,7 +49,8 @@ class StreamableHTTPClientTransport {
+                 serverUrl: this._url,
+                 resourceMetadataUrl: this._resourceMetadataUrl,
+                 scope: this._scope,
+-                fetchFn: this._fetchWithInit
++                fetchFn: this._fetchWithInit,
++                resourceMetadataFetchFn: this._resourceFetchWithInit
+             });
+         }
+         catch (error) {
+@@ -74,10 +77,11 @@ class StreamableHTTPClientTransport {
+             headers['mcp-protocol-version'] = this._protocolVersion;
+         }
+         const extraHeaders = (0, transport_js_1.normalizeHeaders)(this._requestInit?.headers);
+-        return new Headers({
+-            ...headers,
+-            ...extraHeaders
+-        });
++        const result = new Headers(extraHeaders);
++        for (const [name, value] of Object.entries(headers)) {
++            result.set(name, value);
++        }
++        return result;
+     }
+     async _startOrAuthSse(options) {
+         const { resumptionToken } = options;
+@@ -275,7 +279,8 @@ class StreamableHTTPClientTransport {
+             authorizationCode,
+             resourceMetadataUrl: this._resourceMetadataUrl,
+             scope: this._scope,
+-            fetchFn: this._fetchWithInit
++            fetchFn: this._fetchWithInit,
++            resourceMetadataFetchFn: this._resourceFetchWithInit
+         });
+         if (result !== 'AUTHORIZED') {
+             throw new auth_js_1.UnauthorizedError('Failed to authorize');
+@@ -290,7 +295,38 @@ class StreamableHTTPClientTransport {
          this.onclose?.();
      }
      async send(message, options) {
@@ -155,7 +304,7 @@ index a29a7d3a0f14d9cd800ef5b296485237350c666f..c362ae5fe6c62c8c8eae7e2e61de1eed
              const { resumptionToken, onresumptiontoken } = options || {};
              if (resumptionToken) {
                  // If we have at last event ID, we need to reconnect the SSE stream
-@@ -298,6 +329,7 @@ class StreamableHTTPClientTransport {
+@@ -298,6 +334,7 @@ class StreamableHTTPClientTransport {
                  return;
              }
              const headers = await this._commonHeaders();
@@ -163,7 +312,7 @@ index a29a7d3a0f14d9cd800ef5b296485237350c666f..c362ae5fe6c62c8c8eae7e2e61de1eed
              headers.set('content-type', 'application/json');
              headers.set('accept', 'application/json, text/event-stream');
              const init = {
-@@ -310,11 +342,20 @@ class StreamableHTTPClientTransport {
+@@ -310,11 +347,20 @@ class StreamableHTTPClientTransport {
              const response = await (this._fetch ?? fetch)(this._url, init);
              // Handle session ID received during initialization
              const sessionId = response.headers.get('mcp-session-id');
@@ -185,7 +334,17 @@ index a29a7d3a0f14d9cd800ef5b296485237350c666f..c362ae5fe6c62c8c8eae7e2e61de1eed
                  if (response.status === 401 && this._authProvider) {
                      // Prevent infinite recursion when server returns 401 after successful auth
                      if (this._hasCompletedAuthFlow) {
-@@ -335,7 +376,7 @@ class StreamableHTTPClientTransport {
+@@ -327,7 +373,8 @@ class StreamableHTTPClientTransport {
+                         serverUrl: this._url,
+                         resourceMetadataUrl: this._resourceMetadataUrl,
+                         scope: this._scope,
+-                        fetchFn: this._fetchWithInit
++                        fetchFn: this._fetchWithInit,
++                        resourceMetadataFetchFn: this._resourceFetchWithInit
+                     });
+                     if (result !== 'AUTHORIZED') {
+                         throw new auth_js_1.UnauthorizedError();
+@@ -335,7 +382,7 @@ class StreamableHTTPClientTransport {
                      // Mark that we completed auth flow
                      this._hasCompletedAuthFlow = true;
                      // Purposely _not_ awaited, so we don't call onerror twice
@@ -194,7 +353,14 @@ index a29a7d3a0f14d9cd800ef5b296485237350c666f..c362ae5fe6c62c8c8eae7e2e61de1eed
                  }
                  if (response.status === 403 && this._authProvider) {
                      const { resourceMetadataUrl, scope, error } = (0, auth_js_1.extractWWWAuthenticateParams)(response);
-@@ -362,7 +403,7 @@ class StreamableHTTPClientTransport {
+@@ -357,12 +404,13 @@ class StreamableHTTPClientTransport {
+                             serverUrl: this._url,
+                             resourceMetadataUrl: this._resourceMetadataUrl,
+                             scope: this._scope,
+-                            fetchFn: this._fetch
++                            fetchFn: this._fetchWithInit,
++                            resourceMetadataFetchFn: this._resourceFetchWithInit
+                         });
                          if (result !== 'AUTHORIZED') {
                              throw new auth_js_1.UnauthorizedError();
                          }
@@ -204,7 +370,7 @@ index a29a7d3a0f14d9cd800ef5b296485237350c666f..c362ae5fe6c62c8c8eae7e2e61de1eed
                  }
                  throw new StreamableHTTPError(response.status, `Error POSTing to endpoint: ${text}`);
 diff --git a/dist/cjs/shared/protocol.js b/dist/cjs/shared/protocol.js
-index 3617e787f0ba70447c99501aee7aa67584d89758..4a96d6a0328fa348b96f3869ab7e0bb77538182b 100644
+index 3617e787f0ba70447c99501aee7aa67584d89758..4ee4d158391558fdc1f977f5134b7cacfc45e8c3 100644
 --- a/dist/cjs/shared/protocol.js
 +++ b/dist/cjs/shared/protocol.js
 @@ -744,7 +744,12 @@ class Protocol {
@@ -221,8 +387,75 @@ index 3617e787f0ba70447c99501aee7aa67584d89758..4a96d6a0328fa348b96f3869ab7e0bb7
                      this._cleanupTimeout(messageId);
                      reject(error);
                  });
+diff --git a/dist/esm/client/auth.js b/dist/esm/client/auth.js
+index e183040fc2bba22ca1ccc784984f3310854403b7..6b88910ca88f9714abe7cad26fbf3a31c4fb376c 100644
+--- a/dist/esm/client/auth.js
++++ b/dist/esm/client/auth.js
+@@ -161,7 +161,7 @@ export async function auth(provider, options) {
+         throw error;
+     }
+ }
+-async function authInternal(provider, { serverUrl, authorizationCode, scope, resourceMetadataUrl, fetchFn }) {
++async function authInternal(provider, { serverUrl, authorizationCode, scope, resourceMetadataUrl, fetchFn, resourceMetadataFetchFn }) {
+     // Check if the provider has cached discovery state to skip discovery
+     const cachedState = await provider.discoveryState?.();
+     let resourceMetadata;
+@@ -173,6 +173,9 @@ async function authInternal(provider, { serverUrl, authorizationCode, scope, res
+     if (!effectiveResourceMetadataUrl && cachedState?.resourceMetadataUrl) {
+         effectiveResourceMetadataUrl = new URL(cachedState.resourceMetadataUrl);
+     }
++    const protectedResourceFetchFn = !effectiveResourceMetadataUrl || effectiveResourceMetadataUrl.origin === new URL(serverUrl).origin
++        ? (resourceMetadataFetchFn ?? fetchFn)
++        : fetchFn;
+     if (cachedState?.authorizationServerUrl) {
+         // Restore discovery state from cache
+         authorizationServerUrl = cachedState.authorizationServerUrl;
+@@ -182,7 +185,7 @@ async function authInternal(provider, { serverUrl, authorizationCode, scope, res
+         // If resource metadata wasn't cached, try to fetch it for selectResourceURL
+         if (!resourceMetadata) {
+             try {
+-                resourceMetadata = await discoverOAuthProtectedResourceMetadata(serverUrl, { resourceMetadataUrl: effectiveResourceMetadataUrl }, fetchFn);
++                resourceMetadata = await discoverOAuthProtectedResourceMetadata(serverUrl, { resourceMetadataUrl: effectiveResourceMetadataUrl }, protectedResourceFetchFn);
+             }
+             catch {
+                 // RFC 9728 not available — selectResourceURL will handle undefined
+@@ -200,7 +203,11 @@ async function authInternal(provider, { serverUrl, authorizationCode, scope, res
+     }
+     else {
+         // Full discovery via RFC 9728
+-        const serverInfo = await discoverOAuthServerInfo(serverUrl, { resourceMetadataUrl: effectiveResourceMetadataUrl, fetchFn });
++        const serverInfo = await discoverOAuthServerInfo(serverUrl, {
++            resourceMetadataUrl: effectiveResourceMetadataUrl,
++            fetchFn,
++            resourceMetadataFetchFn: protectedResourceFetchFn
++        });
+         authorizationServerUrl = serverInfo.authorizationServerUrl;
+         metadata = serverInfo.authorizationServerMetadata;
+         resourceMetadata = serverInfo.resourceMetadata;
+@@ -663,7 +670,7 @@ export async function discoverOAuthServerInfo(serverUrl, opts) {
+     let resourceMetadata;
+     let authorizationServerUrl;
+     try {
+-        resourceMetadata = await discoverOAuthProtectedResourceMetadata(serverUrl, { resourceMetadataUrl: opts?.resourceMetadataUrl }, opts?.fetchFn);
++        resourceMetadata = await discoverOAuthProtectedResourceMetadata(serverUrl, { resourceMetadataUrl: opts?.resourceMetadataUrl }, opts?.resourceMetadataFetchFn ?? opts?.fetchFn);
+         if (resourceMetadata.authorization_servers && resourceMetadata.authorization_servers.length > 0) {
+             authorizationServerUrl = resourceMetadata.authorization_servers[0];
+         }
+diff --git a/dist/esm/client/index.d.ts b/dist/esm/client/index.d.ts
+index 6f567a193626587a2730b5a49293ca5dfd4181ea..5b7c841c000508e389ce617f559f7c2a5126ca9f 100644
+--- a/dist/esm/client/index.d.ts
++++ b/dist/esm/client/index.d.ts
+@@ -428,6 +428,8 @@ export declare class Client<RequestT extends Request = Request, NotificationT ex
+      *
+      * For task-based execution with streaming behavior, use client.experimental.tasks.callToolStream() instead.
+      */
++    callTool(params: CallToolRequest['params'], resultSchema?: undefined, options?: RequestOptions): Promise<SchemaOutput<typeof CallToolResultSchema>>;
++    callTool<T extends typeof CallToolResultSchema | typeof CompatibilityCallToolResultSchema>(params: CallToolRequest['params'], resultSchema: T, options?: RequestOptions): Promise<SchemaOutput<T>>;
+     callTool(params: CallToolRequest['params'], resultSchema?: typeof CallToolResultSchema | typeof CompatibilityCallToolResultSchema, options?: RequestOptions): Promise<{
+         [x: string]: unknown;
+         content: ({
 diff --git a/dist/esm/client/index.js b/dist/esm/client/index.js
-index 49b12c6cd918c457420fef7ad5528a9443d1a191..2afe2e22e960f26c9d516ef135d89f8eb9e4caff 100644
+index 49b12c6cd918c457420fef7ad5528a9443d1a191..339153cb7e9299b7a9bdec0e56e41cedf425fb31 100644
 --- a/dist/esm/client/index.js
 +++ b/dist/esm/client/index.js
 @@ -284,41 +284,16 @@ export class Client extends Protocol {
@@ -309,8 +542,69 @@ index 49b12c6cd918c457420fef7ad5528a9443d1a191..2afe2e22e960f26c9d516ef135d89f8e
      /**
       * After initialization has completed, this will be populated with the server's reported capabilities.
       */
+diff --git a/dist/esm/client/sse.js b/dist/esm/client/sse.js
+index 58c474156ba4b33090ac092be6f3284e695a7ffd..b813e467b497697208167ad9bfccdecd1200ffac 100644
+--- a/dist/esm/client/sse.js
++++ b/dist/esm/client/sse.js
+@@ -23,7 +23,9 @@ export class SSEClientTransport {
+         this._requestInit = opts?.requestInit;
+         this._authProvider = opts?.authProvider;
+         this._fetch = opts?.fetch;
+-        this._fetchWithInit = createFetchWithInit(opts?.fetch, opts?.requestInit);
++        this._resourceFetchWithInit = createFetchWithInit(opts?.fetch, { ...opts?.requestInit, redirect: 'error' });
++        const oauthRequestInit = opts?.requestInit ? { ...opts.requestInit, headers: undefined } : undefined;
++        this._fetchWithInit = createFetchWithInit(opts?.fetch, oauthRequestInit);
+     }
+     async _authThenStart() {
+         if (!this._authProvider) {
+@@ -35,7 +37,8 @@ export class SSEClientTransport {
+                 serverUrl: this._url,
+                 resourceMetadataUrl: this._resourceMetadataUrl,
+                 scope: this._scope,
+-                fetchFn: this._fetchWithInit
++                fetchFn: this._fetchWithInit,
++                resourceMetadataFetchFn: this._resourceFetchWithInit
+             });
+         }
+         catch (error) {
+@@ -59,10 +62,11 @@ export class SSEClientTransport {
+             headers['mcp-protocol-version'] = this._protocolVersion;
+         }
+         const extraHeaders = normalizeHeaders(this._requestInit?.headers);
+-        return new Headers({
+-            ...headers,
+-            ...extraHeaders
+-        });
++        const result = new Headers(extraHeaders);
++        for (const [name, value] of Object.entries(headers)) {
++            result.set(name, value);
++        }
++        return result;
+     }
+     _startOrAuth() {
+         const fetchImpl = (this?._eventSourceInit?.fetch ?? this._fetch ?? fetch);
+@@ -145,7 +149,8 @@ export class SSEClientTransport {
+             authorizationCode,
+             resourceMetadataUrl: this._resourceMetadataUrl,
+             scope: this._scope,
+-            fetchFn: this._fetchWithInit
++            fetchFn: this._fetchWithInit,
++            resourceMetadataFetchFn: this._resourceFetchWithInit
+         });
+         if (result !== 'AUTHORIZED') {
+             throw new UnauthorizedError('Failed to authorize');
+@@ -181,7 +186,8 @@ export class SSEClientTransport {
+                         serverUrl: this._url,
+                         resourceMetadataUrl: this._resourceMetadataUrl,
+                         scope: this._scope,
+-                        fetchFn: this._fetchWithInit
++                        fetchFn: this._fetchWithInit,
++                        resourceMetadataFetchFn: this._resourceFetchWithInit
+                     });
+                     if (result !== 'AUTHORIZED') {
+                         throw new UnauthorizedError();
 diff --git a/dist/esm/client/streamableHttp.js b/dist/esm/client/streamableHttp.js
-index 624172aa24ae255a67c083f9c19053343e4a0581..ac75b14545fda44aff7ff4d97cc5da884fcc627a 100644
+index 624172aa24ae255a67c083f9c19053343e4a0581..88f7f5c3528d0ce6115efbebfdda98eba7077b8b 100644
 --- a/dist/esm/client/streamableHttp.js
 +++ b/dist/esm/client/streamableHttp.js
 @@ -1,5 +1,5 @@
@@ -320,7 +614,54 @@ index 624172aa24ae255a67c083f9c19053343e4a0581..ac75b14545fda44aff7ff4d97cc5da88
  import { auth, extractWWWAuthenticateParams, UnauthorizedError } from './auth.js';
  import { EventSourceParserStream } from 'eventsource-parser/stream';
  // Default reconnection options for StreamableHTTP connections
-@@ -286,7 +286,38 @@ export class StreamableHTTPClientTransport {
+@@ -29,7 +29,9 @@ export class StreamableHTTPClientTransport {
+         this._requestInit = opts?.requestInit;
+         this._authProvider = opts?.authProvider;
+         this._fetch = opts?.fetch;
+-        this._fetchWithInit = createFetchWithInit(opts?.fetch, opts?.requestInit);
++        this._resourceFetchWithInit = createFetchWithInit(opts?.fetch, { ...opts?.requestInit, redirect: 'error' });
++        const oauthRequestInit = opts?.requestInit ? { ...opts.requestInit, headers: undefined } : undefined;
++        this._fetchWithInit = createFetchWithInit(opts?.fetch, oauthRequestInit);
+         this._sessionId = opts?.sessionId;
+         this._reconnectionOptions = opts?.reconnectionOptions ?? DEFAULT_STREAMABLE_HTTP_RECONNECTION_OPTIONS;
+     }
+@@ -43,7 +45,8 @@ export class StreamableHTTPClientTransport {
+                 serverUrl: this._url,
+                 resourceMetadataUrl: this._resourceMetadataUrl,
+                 scope: this._scope,
+-                fetchFn: this._fetchWithInit
++                fetchFn: this._fetchWithInit,
++                resourceMetadataFetchFn: this._resourceFetchWithInit
+             });
+         }
+         catch (error) {
+@@ -70,10 +73,11 @@ export class StreamableHTTPClientTransport {
+             headers['mcp-protocol-version'] = this._protocolVersion;
+         }
+         const extraHeaders = normalizeHeaders(this._requestInit?.headers);
+-        return new Headers({
+-            ...headers,
+-            ...extraHeaders
+-        });
++        const result = new Headers(extraHeaders);
++        for (const [name, value] of Object.entries(headers)) {
++            result.set(name, value);
++        }
++        return result;
+     }
+     async _startOrAuthSse(options) {
+         const { resumptionToken } = options;
+@@ -271,7 +275,8 @@ export class StreamableHTTPClientTransport {
+             authorizationCode,
+             resourceMetadataUrl: this._resourceMetadataUrl,
+             scope: this._scope,
+-            fetchFn: this._fetchWithInit
++            fetchFn: this._fetchWithInit,
++            resourceMetadataFetchFn: this._resourceFetchWithInit
+         });
+         if (result !== 'AUTHORIZED') {
+             throw new UnauthorizedError('Failed to authorize');
+@@ -286,7 +291,38 @@ export class StreamableHTTPClientTransport {
          this.onclose?.();
      }
      async send(message, options) {
@@ -359,7 +700,7 @@ index 624172aa24ae255a67c083f9c19053343e4a0581..ac75b14545fda44aff7ff4d97cc5da88
              const { resumptionToken, onresumptiontoken } = options || {};
              if (resumptionToken) {
                  // If we have at last event ID, we need to reconnect the SSE stream
-@@ -294,6 +325,7 @@ export class StreamableHTTPClientTransport {
+@@ -294,6 +330,7 @@ export class StreamableHTTPClientTransport {
                  return;
              }
              const headers = await this._commonHeaders();
@@ -367,7 +708,7 @@ index 624172aa24ae255a67c083f9c19053343e4a0581..ac75b14545fda44aff7ff4d97cc5da88
              headers.set('content-type', 'application/json');
              headers.set('accept', 'application/json, text/event-stream');
              const init = {
-@@ -306,11 +338,20 @@ export class StreamableHTTPClientTransport {
+@@ -306,11 +343,20 @@ export class StreamableHTTPClientTransport {
              const response = await (this._fetch ?? fetch)(this._url, init);
              // Handle session ID received during initialization
              const sessionId = response.headers.get('mcp-session-id');
@@ -389,7 +730,17 @@ index 624172aa24ae255a67c083f9c19053343e4a0581..ac75b14545fda44aff7ff4d97cc5da88
                  if (response.status === 401 && this._authProvider) {
                      // Prevent infinite recursion when server returns 401 after successful auth
                      if (this._hasCompletedAuthFlow) {
-@@ -331,7 +372,7 @@ export class StreamableHTTPClientTransport {
+@@ -323,7 +369,8 @@ export class StreamableHTTPClientTransport {
+                         serverUrl: this._url,
+                         resourceMetadataUrl: this._resourceMetadataUrl,
+                         scope: this._scope,
+-                        fetchFn: this._fetchWithInit
++                        fetchFn: this._fetchWithInit,
++                        resourceMetadataFetchFn: this._resourceFetchWithInit
+                     });
+                     if (result !== 'AUTHORIZED') {
+                         throw new UnauthorizedError();
+@@ -331,7 +378,7 @@ export class StreamableHTTPClientTransport {
                      // Mark that we completed auth flow
                      this._hasCompletedAuthFlow = true;
                      // Purposely _not_ awaited, so we don't call onerror twice
@@ -398,7 +749,14 @@ index 624172aa24ae255a67c083f9c19053343e4a0581..ac75b14545fda44aff7ff4d97cc5da88
                  }
                  if (response.status === 403 && this._authProvider) {
                      const { resourceMetadataUrl, scope, error } = extractWWWAuthenticateParams(response);
-@@ -358,7 +399,7 @@ export class StreamableHTTPClientTransport {
+@@ -353,12 +400,13 @@ export class StreamableHTTPClientTransport {
+                             serverUrl: this._url,
+                             resourceMetadataUrl: this._resourceMetadataUrl,
+                             scope: this._scope,
+-                            fetchFn: this._fetch
++                            fetchFn: this._fetchWithInit,
++                            resourceMetadataFetchFn: this._resourceFetchWithInit
+                         });
                          if (result !== 'AUTHORIZED') {
                              throw new UnauthorizedError();
                          }
@@ -408,7 +766,7 @@ index 624172aa24ae255a67c083f9c19053343e4a0581..ac75b14545fda44aff7ff4d97cc5da88
                  }
                  throw new StreamableHTTPError(response.status, `Error POSTing to endpoint: ${text}`);
 diff --git a/dist/esm/shared/protocol.js b/dist/esm/shared/protocol.js
-index bfa2b7120a0f50c569364ea5264e6f811076f44f..abd8dfd707c155f71dae7aeeeeaf7547368ac749 100644
+index bfa2b7120a0f50c569364ea5264e6f811076f44f..dec477d16a0fd796854542c1144279a6e86567f2 100644
 --- a/dist/esm/shared/protocol.js
 +++ b/dist/esm/shared/protocol.js
 @@ -740,7 +740,12 @@ export class Protocol {