diff --git a/src/authentication.test.ts b/src/authentication.test.ts
index 1cfaff7..da9ff85 100644
--- a/src/authentication.test.ts
+++ b/src/authentication.test.ts
@@ -103,15 +103,90 @@ describe("AuthenticationMiddleware", () => {
       expect(body.id).toBe(null);
     });
 
-    it("should have consistent format regardless of configuration", () => {
+    it("should have consistent body format regardless of configuration", () => {
       const middleware1 = new AuthenticationMiddleware({});
       const middleware2 = new AuthenticationMiddleware({ apiKey: "test" });
 
       const response1 = middleware1.getUnauthorizedResponse();
       const response2 = middleware2.getUnauthorizedResponse();
 
-      expect(response1.headers).toEqual(response2.headers);
       expect(response1.body).toEqual(response2.body);
     });
+
+    it("should not include WWW-Authenticate header without OAuth config", () => {
+      const middleware = new AuthenticationMiddleware({ apiKey: "test" });
+      const response = middleware.getUnauthorizedResponse();
+
+      expect(response.headers["WWW-Authenticate"]).toBeUndefined();
+    });
+
+    it("should include WWW-Authenticate header with OAuth config", () => {
+      const middleware = new AuthenticationMiddleware({
+        apiKey: "test",
+        oauth: {
+          protectedResource: {
+            resource: "https://example.com",
+          },
+        },
+      });
+      const response = middleware.getUnauthorizedResponse();
+
+      expect(response.headers["WWW-Authenticate"]).toBe(
+        'Bearer resource_metadata="https://example.com/.well-known/oauth-protected-resource"',
+      );
+    });
+
+    it("should handle OAuth config with trailing slash in resource URL", () => {
+      const middleware = new AuthenticationMiddleware({
+        apiKey: "test",
+        oauth: {
+          protectedResource: {
+            resource: "https://example.com/",
+          },
+        },
+      });
+      const response = middleware.getUnauthorizedResponse();
+
+      expect(response.headers["WWW-Authenticate"]).toBe(
+        'Bearer resource_metadata="https://example.com//.well-known/oauth-protected-resource"',
+      );
+    });
+
+    it("should not include WWW-Authenticate header when OAuth config is empty", () => {
+      const middleware = new AuthenticationMiddleware({
+        apiKey: "test",
+        oauth: {},
+      });
+      const response = middleware.getUnauthorizedResponse();
+
+      expect(response.headers["WWW-Authenticate"]).toBeUndefined();
+    });
+
+    it("should not include WWW-Authenticate header when protectedResource is empty", () => {
+      const middleware = new AuthenticationMiddleware({
+        apiKey: "test",
+        oauth: {
+          protectedResource: {},
+        },
+      });
+      const response = middleware.getUnauthorizedResponse();
+
+      expect(response.headers["WWW-Authenticate"]).toBeUndefined();
+    });
+
+    it("should include WWW-Authenticate header with OAuth config but no apiKey", () => {
+      const middleware = new AuthenticationMiddleware({
+        oauth: {
+          protectedResource: {
+            resource: "https://example.com",
+          },
+        },
+      });
+      const response = middleware.getUnauthorizedResponse();
+
+      expect(response.headers["WWW-Authenticate"]).toBe(
+        'Bearer resource_metadata="https://example.com/.well-known/oauth-protected-resource"',
+      );
+    });
   });
 });
\ No newline at end of file
diff --git a/src/authentication.ts b/src/authentication.ts
index 2784c6a..a66a80f 100644
--- a/src/authentication.ts
+++ b/src/authentication.ts
@@ -2,12 +2,26 @@ import type { IncomingMessage } from "http";
 
 export interface AuthConfig {
   apiKey?: string;
+  oauth?: {
+    protectedResource?: {
+      resource?: string;
+    };
+  };
 }
 
 export class AuthenticationMiddleware {
   constructor(private config: AuthConfig = {}) {}
 
-  getUnauthorizedResponse() {
+  getUnauthorizedResponse(): { body: string; headers: Record<string, string> } {
+    const headers: Record<string, string> = {
+      "Content-Type": "application/json",
+    };
+
+    // Add WWW-Authenticate header if OAuth config is available
+    if (this.config.oauth?.protectedResource?.resource) {
+      headers["WWW-Authenticate"] = `Bearer resource_metadata="${this.config.oauth.protectedResource.resource}/.well-known/oauth-protected-resource"`;
+    }
+
     return {
       body: JSON.stringify({
         error: {
@@ -17,9 +31,7 @@ export class AuthenticationMiddleware {
         id: null,
         jsonrpc: "2.0",
       }),
-      headers: {
-        "Content-Type": "application/json",
-      },
+      headers,
     };
   }
 
diff --git a/src/index.ts b/src/index.ts
index 8d60682..96e5f3c 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,3 +1,5 @@
+export type { AuthConfig } from "./authentication.js";
+export { AuthenticationMiddleware } from "./authentication.js";
 export { InMemoryEventStore } from "./InMemoryEventStore.js";
 export { proxyServer } from "./proxyServer.js";
 export { startHTTPServer } from "./startHTTPServer.js";
diff --git a/src/startHTTPServer.ts b/src/startHTTPServer.ts
index 58f4b3a..2e216c0 100644
--- a/src/startHTTPServer.ts
+++ b/src/startHTTPServer.ts
@@ -8,7 +8,7 @@ import { isInitializeRequest } from "@modelcontextprotocol/sdk/types.js";
 import http from "http";
 import { randomUUID } from "node:crypto";
 
-import { AuthenticationMiddleware } from "./authentication.js";
+import { AuthConfig, AuthenticationMiddleware } from "./authentication.js";
 import { InMemoryEventStore } from "./InMemoryEventStore.js";
 
 export type SSEServer = {
@@ -49,6 +49,17 @@ const createJsonRpcErrorResponse = (code: number, message: string) => {
   });
 };
 
+// Helper function to get WWW-Authenticate header value
+const getWWWAuthenticateHeader = (
+  oauth?: AuthConfig["oauth"],
+): string | undefined => {
+  if (!oauth?.protectedResource?.resource) {
+    return undefined;
+  }
+
+  return `Bearer resource_metadata="${oauth.protectedResource.resource}/.well-known/oauth-protected-resource"`;
+};
+
 // Helper function to handle Response errors and send appropriate HTTP response
 const handleResponseError = (
   error: unknown,
@@ -98,6 +109,7 @@ const handleStreamRequest = async <T extends ServerLike>({
   enableJsonResponse,
   endpoint,
   eventStore,
+  oauth,
   onClose,
   onConnect,
   req,
@@ -113,6 +125,7 @@ const handleStreamRequest = async <T extends ServerLike>({
   enableJsonResponse?: boolean;
   endpoint: string;
   eventStore?: EventStore;
+  oauth?: AuthConfig["oauth"];
   onClose?: (server: T) => Promise<void>;
   onConnect?: (server: T) => Promise<void>;
   req: http.IncomingMessage;
@@ -148,6 +161,13 @@ const handleStreamRequest = async <T extends ServerLike>({
                 : "Unauthorized: Authentication failed";
 
             res.setHeader("Content-Type", "application/json");
+
+            // Add WWW-Authenticate header if OAuth config is available
+            const wwwAuthHeader = getWWWAuthenticateHeader(oauth);
+            if (wwwAuthHeader) {
+              res.setHeader("WWW-Authenticate", wwwAuthHeader);
+            }
+
             res.writeHead(401).end(
               JSON.stringify({
                 error: {
@@ -165,6 +185,13 @@ const handleStreamRequest = async <T extends ServerLike>({
           const errorMessage = error instanceof Error ? error.message : "Unauthorized: Authentication error";
           console.error("Authentication error:", error);
           res.setHeader("Content-Type", "application/json");
+
+          // Add WWW-Authenticate header if OAuth config is available
+          const wwwAuthHeader = getWWWAuthenticateHeader(oauth);
+          if (wwwAuthHeader) {
+            res.setHeader("WWW-Authenticate", wwwAuthHeader);
+          }
+
           res.writeHead(401).end(
             JSON.stringify({
               error: {
@@ -242,6 +269,13 @@ const handleStreamRequest = async <T extends ServerLike>({
 
           if (isAuthError) {
             res.setHeader("Content-Type", "application/json");
+
+            // Add WWW-Authenticate header if OAuth config is available
+            const wwwAuthHeader = getWWWAuthenticateHeader(oauth);
+            if (wwwAuthHeader) {
+              res.setHeader("WWW-Authenticate", wwwAuthHeader);
+            }
+
             res.writeHead(401).end(JSON.stringify({
               error: {
                 code: -32000,
@@ -294,6 +328,13 @@ const handleStreamRequest = async <T extends ServerLike>({
 
           if (isAuthError) {
             res.setHeader("Content-Type", "application/json");
+
+            // Add WWW-Authenticate header if OAuth config is available
+            const wwwAuthHeader = getWWWAuthenticateHeader(oauth);
+            if (wwwAuthHeader) {
+              res.setHeader("WWW-Authenticate", wwwAuthHeader);
+            }
+
             res.writeHead(401).end(JSON.stringify({
               error: {
                 code: -32000,
@@ -549,6 +590,7 @@ export const startHTTPServer = async <T extends ServerLike>({
   enableJsonResponse,
   eventStore,
   host = "::",
+  oauth,
   onClose,
   onConnect,
   onUnhandledRequest,
@@ -563,6 +605,7 @@ export const startHTTPServer = async <T extends ServerLike>({
   enableJsonResponse?: boolean;
   eventStore?: EventStore;
   host?: string;
+  oauth?: AuthConfig["oauth"];
   onClose?: (server: T) => Promise<void>;
   onConnect?: (server: T) => Promise<void>;
   onUnhandledRequest?: (
@@ -584,7 +627,7 @@ export const startHTTPServer = async <T extends ServerLike>({
     }
   > = {};
 
-  const authMiddleware = new AuthenticationMiddleware({ apiKey });
+  const authMiddleware = new AuthenticationMiddleware({ apiKey, oauth });
 
   /**
    * @author https://dev.classmethod.jp/articles/mcp-sse/
@@ -647,6 +690,7 @@ export const startHTTPServer = async <T extends ServerLike>({
         enableJsonResponse,
         endpoint: streamEndpoint,
         eventStore,
+        oauth,
         onClose,
         onConnect,
         req,