Add graceful degradation when auth server unavailable

Server starts immediately and retries auth connection in background.
Splash page and health endpoint remain accessible in degraded mode.

auth-server/src/index.ts

@@ -14,7 +14,7 @@ console.log('=====================================');
 console.log('MCP Demonstration Authorization Server');
 console.log('=====================================');
 console.log('This standalone server demonstrates OAuth 2.0');
-console.log('authorization separate from the MCP resource server');
+console.log('authorization for the MCP resource server');
 console.log('');
 console.log('This is for demonstration purposes only.');
 console.log('In production, you would use a real OAuth provider');

mcp-server/src/index.ts

@@ -17,6 +17,7 @@ import { getOAuthProtectedResourceMetadataUrl, mcpAuthMetadataRouter } from "@mo
 import cors from "cors";
 import rateLimit from "express-rate-limit";
 import express from "express";
+import fs from "fs";
 import path from "path";
 import { fileURLToPath } from "url";
 import { ExternalAuthVerifier } from "./auth/external-verifier.js";
@@ -141,71 +142,59 @@ const staticFileRateLimit = rateLimit({
   message: { error: 'too_many_requests', error_description: 'Static file rate limit exceeded' }
 });
 
-// Separate mode: MCP server uses external auth server
+// MCP server using external auth server
-logger.info('Starting MCP server in SEPARATE mode', {
+logger.info('Starting MCP server', {
   baseUri: BASE_URI,
   port: PORT,
   authServerUrl: AUTH_SERVER_URL
 });
 
-// Fetch metadata from external auth server with retry logic
+// Auth server state - will be populated asynchronously
-let authMetadata;
+let authMetadata: any;
-const maxRetries = 5;
+let authServerAvailable = false;
-const retryDelay = 3000; // 3 seconds
 
-for (let attempt = 1; attempt <= maxRetries; attempt++) {
+// OAuth metadata endpoint - responds based on current auth server status
-  try {
+app.get('/.well-known/oauth-authorization-server', (req, res) => {
-    logger.info(`Attempting to connect to auth server (attempt ${attempt}/${maxRetries})`, {
+  if (authServerAvailable && authMetadata) {
-      authServerUrl: AUTH_SERVER_URL
+    // Return the auth server metadata
-    });
+    res.json(authMetadata);
-
-    const authMetadataResponse = await fetch(`${AUTH_SERVER_URL}/.well-known/oauth-authorization-server`);
-    if (!authMetadataResponse.ok) {
-      throw new Error(`Failed to fetch auth server metadata: ${authMetadataResponse.status} ${authMetadataResponse.statusText}`);
-    }
-    authMetadata = await authMetadataResponse.json();
-    logger.info('Successfully fetched auth server metadata', {
-      issuer: authMetadata.issuer,
-      authorizationEndpoint: authMetadata.authorization_endpoint,
-      tokenEndpoint: authMetadata.token_endpoint
-    });
-    break; // Success, exit retry loop
-
-  } catch (error) {
-    if (attempt < maxRetries) {
-      logger.info(`Failed to connect to auth server, retrying in ${retryDelay/1000} seconds...`, {
-        attempt,
-        maxRetries,
-        error: (error as Error).message
-      });
-      await new Promise(resolve => setTimeout(resolve, retryDelay));
   } else {
-      logger.error('Failed to fetch auth server metadata after all retries', error as Error);
+    // Auth server unavailable
-      logger.error('Make sure the auth server is running at', undefined, { authServerUrl: AUTH_SERVER_URL });
+    res.status(503).json({
-      process.exit(1);
+      error: 'service_unavailable',
+      error_description: 'Authentication server is currently unavailable. Please try again later.'
+    });
   }
+});
+
+// Configure bearer auth middleware that checks auth availability dynamically
+const bearerAuth: express.RequestHandler = (req, res, next) => {
+  if (!authServerAvailable) {
+    // Degraded mode: return 503 for protected endpoints
+    res.status(503).json({
+      jsonrpc: '2.0',
+      error: {
+        code: -32000,
+        message: 'Authentication service unavailable',
+        data: {
+          authServerUrl: AUTH_SERVER_URL,
+          hint: 'The authentication server is not responding. Please ensure it is running and try again.'
         }
+      },
+      id: null
+    });
+    return;
   }
 
-// BACKWARDS COMPATIBILITY: We serve OAuth metadata from the MCP server even in separate mode
+  // Auth is available, use the real bearer auth middleware
-// This is technically redundant since the auth server handles all OAuth operations,
-// but some clients may expect to find .well-known/oauth-authorization-server on the
-// resource server itself. The metadata points to the external auth server endpoints.
-app.use(mcpAuthMetadataRouter({
-  oauthMetadata: authMetadata,
-  resourceServerUrl: new URL(BASE_URI),
-  resourceName: "MCP Feature Reference Server"
-}));
-
-// Configure bearer auth with external verifier
   const externalVerifier = new ExternalAuthVerifier(AUTH_SERVER_URL);
-
   const bearerAuthOptions: BearerAuthMiddlewareOptions = {
     verifier: externalVerifier,
     resourceMetadataUrl: getOAuthProtectedResourceMetadataUrl(new URL(BASE_URI)),
   };
-
+  const realBearerAuth = requireBearerAuth(bearerAuthOptions);
-const bearerAuth = requireBearerAuth(bearerAuthOptions);
+  realBearerAuth(req, res, next);
+};
 
 // MCP routes (legacy SSE transport)
 app.get("/sse", cors(corsOptions), bearerAuth, sseHeaders, handleSSEConnection);
@@ -216,6 +205,19 @@ app.get("/mcp", cors(corsOptions), bearerAuth, handleStreamableHTTP);
 app.post("/mcp", cors(corsOptions), bearerAuth, handleStreamableHTTP);
 app.delete("/mcp", cors(corsOptions), bearerAuth, handleStreamableHTTP);
 
+// Health check endpoint
+app.get("/health", (req, res) => {
+  res.json({
+    status: authServerAvailable ? 'healthy' : 'degraded',
+    services: {
+      mcp: 'operational',
+      auth: authServerAvailable ? 'operational' : 'unavailable',
+      redis: 'operational' // Will be checked if Redis connection fails
+    },
+    authServerUrl: AUTH_SERVER_URL
+  });
+});
+
 // Static assets
 app.get("/mcp-logo.png", staticFileRateLimit, (req, res) => {
   const logoPath = path.join(__dirname, "static", "mcp.png");
@@ -231,7 +233,23 @@ app.get("/styles.css", staticFileRateLimit, (req, res) => {
 // Splash page
 app.get("/", staticFileRateLimit, (req, res) => {
   const splashPath = path.join(__dirname, "static", "index.html");
+
+  if (!authServerAvailable) {
+    // Inject warning banner for degraded mode
+    let html = fs.readFileSync(splashPath, 'utf8');
+    const warningBanner = `
+    <div style="background: #ff6b6b; color: white; padding: 16px; text-align: center; font-weight: bold; border-bottom: 3px solid #c92a2a;">
+      ⚠️ Authentication Service Unavailable - Server Running in Degraded Mode
+      <div style="font-weight: normal; margin-top: 8px; font-size: 14px;">
+        The authentication server at ${AUTH_SERVER_URL} is not responding.
+        MCP endpoints will return errors until the auth server is available.
+      </div>
+    </div>`;
+    html = html.replace('<body>', `<body>${warningBanner}`);
+    res.send(html);
+  } else {
     res.sendFile(splashPath);
+  }
 });
 
 // Note: Fake upstream auth routes are not needed in separate mode
@@ -250,4 +268,51 @@ app.listen(PORT, () => {
     url: `http://localhost:${PORT}`,
     environment: process.env.NODE_ENV || 'development'
   });
+
+  // Try to connect to auth server in background (don't block server startup)
+  connectToAuthServer();
 });
+
+// Attempt to connect to auth server with retries
+async function connectToAuthServer() {
+  const maxRetries = 5;
+  const retryDelay = 3000; // 3 seconds
+
+  for (let attempt = 1; attempt <= maxRetries; attempt++) {
+    try {
+      logger.info(`Attempting to connect to auth server (attempt ${attempt}/${maxRetries})`, {
+        authServerUrl: AUTH_SERVER_URL
+      });
+
+      const authMetadataResponse = await fetch(`${AUTH_SERVER_URL}/.well-known/oauth-authorization-server`);
+      if (!authMetadataResponse.ok) {
+        throw new Error(`Failed to fetch auth server metadata: ${authMetadataResponse.status} ${authMetadataResponse.statusText}`);
+      }
+      authMetadata = await authMetadataResponse.json();
+      authServerAvailable = true;
+      logger.info('Successfully connected to auth server', {
+        issuer: authMetadata.issuer,
+        authorizationEndpoint: authMetadata.authorization_endpoint,
+        tokenEndpoint: authMetadata.token_endpoint
+      });
+      break; // Success, exit retry loop
+
+    } catch (error) {
+      if (attempt < maxRetries) {
+        logger.info(`Failed to connect to auth server, retrying in ${retryDelay/1000} seconds...`, {
+          attempt,
+          maxRetries,
+          error: (error as Error).message
+        });
+        await new Promise(resolve => setTimeout(resolve, retryDelay));
+      } else {
+        logger.error('Failed to connect to auth server after all retries', error as Error);
+        logger.warning('MCP server running in degraded mode - authentication unavailable', {
+          authServerUrl: AUTH_SERVER_URL
+        });
+        logger.warning('Protected endpoints will return 503 until auth server is available');
+        // Server continues in degraded mode
+      }
+    }
+  }
+}