Merge pull request #966 from olaservo/fix/streamable-http-401-handling

fix: detect 401 errors from StreamableHTTP transport for OAuth flow

Author: cliffhall

server/src/index.ts

@@ -17,7 +17,10 @@ import {
   StdioClientTransport,
   getDefaultEnvironment,
 } from "@modelcontextprotocol/sdk/client/stdio.js";
-import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js";
+import {
+  StreamableHTTPClientTransport,
+  StreamableHTTPError,
+} from "@modelcontextprotocol/sdk/client/streamableHttp.js";
 import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
 import { SSEServerTransport } from "@modelcontextprotocol/sdk/server/sse.js";
 import { Transport } from "@modelcontextprotocol/sdk/shared/transport.js";
@@ -44,6 +47,22 @@ const { values } = parseArgs({
   },
 });
 
+/**
+ * Helper function to detect 401 Unauthorized errors from various transport types.
+ * StreamableHTTPClientTransport throws a generic Error with "HTTP 401" in the message
+ * when there's no authProvider configured, while SSEClientTransport throws SseError.
+ */
+const is401Error = (error: unknown): boolean => {
+  if (error instanceof SseError && error.code === 401) return true;
+  if (error instanceof StreamableHTTPError && error.code === 401) return true;
+  if (
+    error instanceof Error &&
+    (error.message.includes("HTTP 401") || error.message.includes("(401)"))
+  )
+    return true;
+  return false;
+};
+
 // Function to get HTTP headers.
 const getHttpHeaders = (req: express.Request): Record<string, string> => {
   const headers: Record<string, string> = {};
@@ -508,10 +527,10 @@ app.post(
           req.body,
         );
       } catch (error) {
-        if (error instanceof SseError && error.code === 401) {
+        if (is401Error(error)) {
           console.error(
             "Received 401 Unauthorized from MCP server:",
-            error.message,
+            error instanceof Error ? error.message : error,
           );
           res.status(401).json(error);
           return;
@@ -649,7 +668,7 @@ app.get(
         transportToServer: serverTransport,
       });
     } catch (error) {
-      if (error instanceof SseError && error.code === 401) {
+      if (is401Error(error)) {
         console.error(
           "Received 401 Unauthorized from MCP server. Authentication failure.",
         );
@@ -695,7 +714,7 @@ app.get(
         transportToServer: serverTransport,
       });
     } catch (error) {
-      if (error instanceof SseError && error.code === 401) {
+      if (is401Error(error)) {
         console.error(
           "Received 401 Unauthorized from MCP server. Authentication failure.",
         );