feat: support custom HTTP headers from tool parameters in OneMcpServer

CHANGELOG.md

@@ -1,3 +1,4 @@
 - Added `appcheck:providers:list`, `appcheck:providers:get` and `appcheck:providers:set` to configure App Check attestation providers for an app.
 - Added `appcheck:apps:list` to show every app with its configured App Check providers.
-- Added web app support for Crashlytics MCP tools and prompts.>>>>>>> main
+- Added web app support for Crashlytics MCP tools and prompts.
+- Added support for forwarding custom HTTP headers (`Mcp-Param-*`) to remote MCP tools when defined in tool parameter input schemas (`x-mcp-header`), per [SEP-2243](https://modelcontextprotocol.io/seps/2243-http-standardization).

src/mcp/onemcp/onemcp_server.spec.ts

@@ -53,7 +53,7 @@
         feature: "auth",
       });
       expect(clientRequestStub).to.have.been.calledOnce;
       expect(clientRequestStub.firstCall.args[0].headers).to.deep.include({
         "MCP-Protocol-Version": LATEST_PROTOCOL_VERSION,
         "Mcp-Method": "tools/list",
       });
@@ -104,7 +104,7 @@
   });
 
   describe("callTool", () => {
     const mockContext: any = {
       projectId: "test-project",
     };
 
@@ -122,11 +122,11 @@
         body: { result: mockCallResult },
       });
 
       const result = await tool.fn({ arg: "val" }, mockContext);
 
       expect(result).to.deep.equal(mockCallResult);
       expect(ensureStub).to.have.been.calledOnceWith(
         mockContext.projectId,
         serverUrl,
         feature,
         true,
@@ -143,7 +143,7 @@
           id: 1,
         },
       });
       expect(clientRequestStub.secondCall.args[0].headers).to.deep.include({
         "MCP-Protocol-Version": LATEST_PROTOCOL_VERSION,
         "Mcp-Method": "tools/call",
         "Mcp-Name": "test_tool",
@@ -151,6 +151,44 @@
       });
     });
 
+    it("should include Mcp-Param-X HTTP headers when tool inputSchema defines x-mcp-header", async () => {
+      const mockMcpTool = {
+        name: "execute_sql",
+        inputSchema: {
+          type: "object",
+          properties: {
+            region: {
+              type: "string",
+              "x-mcp-header": "Region",
+            },
+            query: {
+              type: "string",
+            },
+          },
+        },
+      };
+      clientRequestStub.onFirstCall().resolves({
+        body: { result: { tools: [mockMcpTool] } },
+      });
+
+      const tools = await server.listTools();
+      const tool = tools[0];
+
+      clientRequestStub.onSecondCall().resolves({
+        body: { result: { content: [] } },
+      });
+
+      await tool.fn({ region: "us-west1", query: "SELECT 1" }, mockContext);
+
+      expect(clientRequestStub.secondCall.args[0].headers).to.deep.include({
+        "MCP-Protocol-Version": LATEST_PROTOCOL_VERSION,
+        "Mcp-Method": "tools/call",
+        "Mcp-Name": "execute_sql",
+        "x-goog-user-project": "test-project",
+        "Mcp-Param-Region": "us-west1",
+      });
+    });
+
     it("should proxy tool call without x-goog-user-project header if projectId is missing", async () => {
       const mockMcpTool = { name: "test_tool", inputSchema: { type: "object", properties: {} } };
       clientRequestStub.onFirstCall().resolves({
@@ -164,10 +202,10 @@
         body: { result: { content: [] } },
       });
 
       await tool.fn({ arg: "val" }, { ...mockContext, projectId: undefined });
 
       expect(clientRequestStub.secondCall.args[0].headers?.["x-goog-user-project"]).to.be.undefined;
       expect(clientRequestStub.secondCall.args[0].headers).to.deep.equal({
         "MCP-Protocol-Version": LATEST_PROTOCOL_VERSION,
         "Mcp-Method": "tools/call",
         "Mcp-Name": "test_tool",
@@ -240,7 +278,7 @@
 
       const fn = (serverWithFilter as any).callTool.bind(serverWithFilter);
 
-      await expect(fn("disallowed_tool", {}, mockContext)).to.be.rejectedWith(
+      await expect(fn("disallowed_tool", undefined, {}, mockContext)).to.be.rejectedWith(
         FirebaseError,
         /is not allowed on remote server/,
       );

src/mcp/onemcp/onemcp_server.ts

@@ -7,6 +7,7 @@ import {
   ListToolsRequest,
   CallToolRequest,
   LATEST_PROTOCOL_VERSION,
+  Tool,
 } from "@modelcontextprotocol/sdk/types.js";
 import { Client } from "../../apiv2";
 import { ServerTool, ServerToolMeta } from "../tool";
@@ -96,7 +97,7 @@ export class OneMcpServer {
             [x: string]: unknown;
           },
           ctx: McpContext,
-        ) => this.callTool(mcpTool.name, args, ctx),
+        ) => this.callTool(mcpTool.name, mcpTool.inputSchema, args, ctx),
         isAvailable: () => Promise.resolve(true),
       }));
     } catch (error) {
@@ -111,6 +112,7 @@ export class OneMcpServer {
    */
   private async callTool(
     toolName: string,
+    inputSchema: Tool["inputSchema"] | undefined,
     args: {
       [x: string]: unknown;
     },
@@ -126,6 +128,20 @@ export class OneMcpServer {
       );
     }
 
+    const paramHeaders: Record<string, string> = {};
+    const props = inputSchema?.properties;
+    if (props && typeof props === "object" && args) {
+      for (const [paramName, propSchema] of Object.entries(props)) {
+        if (propSchema && typeof propSchema === "object" && "x-mcp-header" in propSchema) {
+          const headerName = (propSchema as Record<string, unknown>)["x-mcp-header"];
+          const argValue = args[paramName];
+          if (argValue !== undefined && argValue !== null) {
+            paramHeaders[`Mcp-Param-${headerName}`] = String(argValue);
+          }
+        }
+      }
+    }
+
     // TODO: Optimize this to not call ensure on every tool call.
     await ensure(ctx.projectId, this.serverUrl, this.feature, /* silent=*/ true);
     try {
@@ -149,6 +165,7 @@ export class OneMcpServer {
             "Mcp-Method": "tools/call",
             "Mcp-Name": toolName,
             ...(ctx.projectId ? { "x-goog-user-project": ctx.projectId } : {}),
+            ...paramHeaders,
           },
         },
       );