Add Hono utilities and example

README.md

@@ -29,6 +29,7 @@ For detailed implementation guides and examples specific to your framework, see:
 
 - **[Express.js Integration](./express/README.md)** - Complete guide for building MCP servers with Express.js
 - **[Next.js Integration](./next/README.md)** - Complete guide for building both MCP servers and clients with Next.js
+- **[Hono Integration](./hono/README.md)** - Complete guide for building MCP servers with Hono
 
 ### Table of Contents
 

hono/README.md

@@ -0,0 +1,251 @@
+# MCP Tools - Hono Integration
+
+Hono utilities for building MCP servers with authentication support. These tools make it easy to add MCP (Model Context Protocol) endpoints to your existing Hono applications.
+
+## Installation
+
+Make sure you have the required dependencies installed:
+
+```bash
+npm install @clerk/mcp-tools hono mcp-lite
+```
+
+If you're using Clerk for authentication, also install the Clerk backend SDK:
+
+```bash
+npm install @clerk/backend
+```
+
+## Quick Start
+
+### Example with Clerk Authentication
+
+Here's a complete example using Clerk for authentication:
+
+```ts
+import Hono from "hono";
+import { logger } from "hono/logger";
+// Hono with auth does not play nicely with @modelcontextprotocol/sdk yet, so we use the mcp-lite package
+import { McpServer } from "mcp-lite";
+import { createClerkClient } from "@clerk/backend";
+import {
+  mcpAuthClerk,
+  protectedResourceHandlerClerk,
+  authServerMetadataHandlerClerk,
+} from "@clerk/mcp-tools/hono";
+
+type AppType = {
+  Bindings: {
+    CLERK_SECRET_KEY: string;
+    CLERK_PUBLISHABLE_KEY: string;
+  }
+};
+
+const app = new Hono<AppType>();
+
+const server = new McpServer({
+  name: "clerk-mcp-server",
+  version: "1.0.0",
+});
+
+server.tool(
+  "get_clerk_user_data",
+  {
+    description: "Gets data about the Clerk user that authorized this request"
+    handler: async (_, { authInfo, ...mcpContext }) => {
+      const clerkAuthInfo = authInfo;
+
+      const clerk = createClerkClient({ secretKey: mcpContext.state.CLERK_SECRET_KEY! });
+
+      if (!clerkAuthInfo?.userId) {
+        return {
+          content: [{ type: "text", text: "Error: user not authenticated" }],
+        };
+      }
+
+      const user = await clerk.users.getUser(clerkAuthInfo.userId);
+      return {
+        content: [{ type: "text", text: JSON.stringify(user) }],
+      };
+    }
+  }
+);
+
+app.use(logger());
+
+app.on(
+  ["GET", "OPTIONS"],
+  "/.well-known/oauth-protected-resource",
+  oauthCorsMiddleware, // <-- cors middleware is helpful for testing in the inspector
+  protectedResourceHandlerClerk()
+);
+app.on(
+  ["GET", "OPTIONS"],
+  "/.well-known/oauth-protected-resource/mcp",
+  oauthCorsMiddleware,
+  protectedResourceHandlerClerk({
+    scopes_supported: ["profile", "email"],
+  })
+);
+app.on(
+  ["GET", "OPTIONS"],
+  "/.well-known/oauth-authorization-server",
+  oauthCorsMiddleware,
+  authServerMetadataHandlerClerk
+);
+
+app.post("/mcp", mcpAuthClerk, async (c) => {
+  const authInfo = c.get("auth");
+  const transport = new StreamableHttpTransport();
+  const mcpHttpHandler = transport.bind(server);
+  const response = await mcpHttpHandler(c.req.raw, { authInfo });
+  return response;
+});
+
+export default app;
+```
+
+
+
+## Authentication Middleware
+
+### `mcpAuthClerk`
+
+Pre-configured authentication middleware for Clerk that automatically handles OAuth token verification.
+
+**Example:**
+
+```ts
+import { mcpAuthClerk } from "@clerk/mcp-tools/hono";
+
+// No additional configuration needed - uses Clerk's built-in token verification
+app.post("/mcp", mcpAuthClerk, /** your mcp server handler */);
+```
+
+This middleware automatically:
+
+- Verifies OAuth access tokens using Clerk
+- Handles authentication state
+- Adds Clerk auth data to request context via `c.get("auth")`
+
+## Protected Resource Metadata
+
+### `protectedResourceHandlerClerk`
+
+Hono handler that returns OAuth protected resource metadata for Clerk integration, as required by [RFC 9728](https://datatracker.ietf.org/doc/html/rfc9728).
+
+**Example:**
+
+```ts
+import { protectedResourceHandlerClerk } from "@clerk/mcp-tools/hono";
+
+app.get(
+  "/.well-known/oauth-protected-resource",
+  protectedResourceHandlerClerk({ scopes_supported: ["email"] })
+);
+```
+
+## Authorization Server Metadata
+
+### `authServerMetadataHandlerClerk`
+
+Hono handler that returns OAuth authorization server metadata for Clerk integration, as defined by [RFC 8414](https://datatracker.ietf.org/doc/html/rfc8414). This endpoint provides clients with information about Clerk's OAuth authorization server capabilities and endpoints.
+
+**Example:**
+
+```ts
+import { authServerMetadataHandlerClerk } from "@clerk/mcp-tools/hono";
+
+// Serve authorization server metadata at the standard well-known location
+app.get(
+  "/.well-known/oauth-authorization-server",
+  authServerMetadataHandlerClerk
+);
+```
+
+**Note:** This handler requires the `CLERK_PUBLISHABLE_KEY` environment variable to be set, as it uses Clerk's public configuration to generate the metadata.
+
+
+## Accessing Authentication Data in Tools
+
+Passing authentication data to your MCP tools is done via the `authInfo` parameter in the tool handler.
+
+The `@modelcontextprotocol/sdk` package requires that you do this by monkeypatching an `Express.Request` object, however, so it does not play nicely with Hono.
+
+The existing Hono MCP middleware does not yet support passing auth to MCP servers, but there is an open PR to add this support: https://github.com/honojs/middleware/pull/1318/files
+
+Alternative libraries like [`mcp-lite`](https://github.com/fiberplane/mcp) (used in the example above) do support the `authInfo` parameter, provided you pass it to the MCP server HTTP handler.
+
+```typescript
+import { McpServer } from "mcp-lite";
+
+const server = new McpServer({
+  name: "my-server",
+  version: "1.0.0",
+});
+
+server.tool(
+  "my-tool",
+  "My tool",
+  { type: "object", properties: {} },
+  async (args, { authInfo }) => {
+    return { content: [{ type: "text", text: `Hello, ${authInfo.extra.userId}!` }] };
+  }
+);
+
+app.post("/mcp", mcpAuthClerk, async (c) => {
+  const authInfo = c.get("auth");
+  const transport = new StreamableHttpTransport();
+  const mcpHttpHandler = transport.bind(server);
+  // pass the authInfo to the MCP server HTTP handler, making it available to the tool handlers
+  const response = await mcpHttpHandler(c.req.raw, { authInfo });
+  return response;
+});
+```
+
+## Environment Variables
+
+When using Clerk integration, make sure to set:
+
+```bash
+CLERK_PUBLISHABLE_KEY=pk_test_...
+CLERK_SECRET_KEY=sk_test_...
+```
+
+The publishable key is used for generating OAuth metadata, while the secret key is used for server-side API calls to fetch user data.
+
+## Error Handling
+
+The middleware automatically handles common authentication errors:
+
+- **Missing Authorization header**: Returns 401 with `WWW-Authenticate` header pointing to your protected resource metadata
+- **Invalid token format**: Throws an error with details about the expected format
+- **Token verification failure**: Returns 401 with error details
+
+## Integration with Existing Hono Apps
+
+These utilities are designed to integrate seamlessly with existing Hono applications. You can:
+
+- Add MCP endpoints to existing routes
+- Use your existing authentication middleware alongside MCP auth
+- Combine with other Hono middleware (CORS, rate limiting, etc.)
+
+```ts
+import cors from "cors";
+import { rateLimiter } from "hono-rate-limiter";
+
+// Apply middleware in the order you need
+app.use(cors());
+app.use(
+  rateLimiter({
+    windowMs: 15 * 60 * 1000,
+    limit: 100,
+  })
+);
+
+app.post(
+  "/mcp",
+  mcpAuthClerk, // MCP authentication
+  /** your mcp server handler */
+);
+```

hono/auth.ts

@@ -0,0 +1,68 @@
+import { createClerkClient } from "@clerk/backend";
+import { TokenType } from "@clerk/backend/internal";
+import type { AuthInfo } from "@modelcontextprotocol/sdk/server/auth/types.js";
+import { env } from "hono/adapter";
+import { createMiddleware } from "hono/factory";
+import { getPRMUrl } from "./utils.js";
+import { verifyClerkToken } from "../server";
+
+/**
+ * Hono middleware that enforces authentication for MCP requests using Clerk.
+ *
+ * Sets an "auth" variable on the request context, which matches the {@link AuthInfo} type from the MCP SDK.
+ */
+export const mcpAuthClerk = createMiddleware<
+  { Variables: { auth: AuthInfo } }
+>(async (c, next) => {
+  const authHeader = c.req.header("Authorization");
+  const [type, token] = authHeader?.split(" ") || [];
+  const bearerToken = type?.toLowerCase() === "bearer" ? token : undefined;
+
+  // Return 401 with proper www-authenticate header if no authorization is provided
+  if (!bearerToken) {
+    // Get the resource metadata url for the protected resource
+    // We return this in the `WWW-Authenticate` header so the MCP client knows where to find the protected resource metadata
+    const resourceMetadataUrl = getPRMUrl(c.req.raw);
+    c.header(
+      "WWW-Authenticate",
+      // NOTE - The mcp sdk also adds `error` and `error_description` to this header as well, depending on the error
+      //        see: https://github.com/modelcontextprotocol/typescript-sdk/blob/b28c297184cb0cb64611a3357d6438dd1b0824c6/src/server/auth/middleware/bearerAuth.ts#L76C1-L95C8
+      `Bearer resource_metadata="${resourceMetadataUrl}"`,
+    );
+    return c.json({ error: "Unauthorized" }, 401);
+  }
+
+  try {
+    const secretKey = (env(c)?.CLERK_SECRET_KEY || "") as string;
+    const publishableKey = (env(c)?.CLERK_PUBLISHABLE_KEY || "") as string;
+
+    const clerkClient = createClerkClient({
+      secretKey,
+      publishableKey,
+    });
+
+    const requestState = await clerkClient.authenticateRequest(c.req.raw, {
+      secretKey,
+      publishableKey,
+      acceptsToken: TokenType.OAuthToken,
+    });
+
+    // This is the result of the authenticateRequest call, with the `TokenType.OAuthToken` type
+    const auth = requestState.toAuth();
+
+    const authInfo = verifyClerkToken(auth, token);
+
+    // Require valid auth for this endpoint
+    if (!authInfo) {
+      return c.json({ error: "Unauthorized" }, 401);
+    }
+
+    // Attach auth to Request and Hono context for downstream handlers
+    c.set("auth", authInfo);
+
+    await next();
+  } catch (error) {
+    console.error("Unexpected mcp auth middleware error:", error);
+    return c.json({ error: "Internal Server Error" }, 500);
+  }
+});

hono/index.ts

@@ -0,0 +1,6 @@
+export { mcpAuthClerk } from "./auth.js";
+export {
+  oauthCorsMiddleware,
+  protectedResourceHandlerClerk,
+  authServerMetadataHandlerClerk,
+} from "./oauth-server-routes.js";