Merge branch 'main' into normalize-connection-logging

Author: cliffhall

README.md

@@ -4,6 +4,15 @@ The MCP inspector is a developer tool for testing and debugging MCP servers.
 
 ![MCP Inspector Screenshot](https://raw.githubusercontent.com/modelcontextprotocol/inspector/main/mcp-inspector.png)
 
+## Architecture Overview
+
+The MCP Inspector consists of two main components that work together:
+
+- **MCP Inspector Client (MCPI)**: A React-based web UI that provides an interactive interface for testing and debugging MCP servers
+- **MCP Proxy (MCPP)**: A Node.js server that acts as a protocol bridge, connecting the web UI to MCP servers via various transport methods (stdio, SSE, streamable-http)
+
+Note that the proxy is not a network proxy for intercepting traffic. Instead, it functions as both an MCP client (connecting to your MCP server) and an HTTP server (serving the web UI), enabling browser-based interaction with MCP servers that use different transport protocols.
+
 ## Running the Inspector
 
 ### Requirements

client/src/lib/hooks/useConnection.ts

@@ -308,7 +308,14 @@ export function useConnection({
         bearerToken || (await serverAuthProvider.tokens())?.access_token;
       if (token) {
         const authHeaderName = headerName || "Authorization";
-        headers[authHeaderName] = `Bearer ${token}`;
+
+        // Add custom header name as a special request header to let the server know which header to pass through
+        if (authHeaderName.toLowerCase() !== "authorization") {
+          headers[authHeaderName] = token;
+          headers["x-custom-auth-header"] = authHeaderName;
+        } else {
+          headers[authHeaderName] = `Bearer ${token}`;
+        }
       }
 
       // Create appropriate transport

server/src/index.ts

@@ -41,6 +41,44 @@ const { values } = parseArgs({
   },
 });
 
+// Function to get HTTP headers.
+// Supports only "sse" and "streamable-http" transport types.
+const getHttpHeaders = (
+  req: express.Request,
+  transportType: string,
+): HeadersInit => {
+  const headers: HeadersInit = {
+    Accept:
+      transportType === "sse"
+        ? "text/event-stream"
+        : "text/event-stream, application/json",
+  };
+  const defaultHeaders =
+    transportType === "sse"
+      ? SSE_HEADERS_PASSTHROUGH
+      : STREAMABLE_HTTP_HEADERS_PASSTHROUGH;
+
+  for (const key of defaultHeaders) {
+    if (req.headers[key] === undefined) {
+      continue;
+    }
+
+    const value = req.headers[key];
+    headers[key] = Array.isArray(value) ? value[value.length - 1] : value;
+  }
+
+  // If the header "x-custom-auth-header" is present, use its value as the custom header name.
+  if (req.headers["x-custom-auth-header"] !== undefined) {
+    const customHeaderName = req.headers["x-custom-auth-header"] as string;
+    const lowerCaseHeaderName = customHeaderName.toLowerCase();
+    if (req.headers[lowerCaseHeaderName] !== undefined) {
+      const value = req.headers[lowerCaseHeaderName];
+      headers[customHeaderName] = value as string;
+    }
+  }
+  return headers;
+};
+
 const app = express();
 app.use(cors());
 app.use((req, res, next) => {
@@ -78,18 +116,8 @@ const createTransport = async (req: express.Request): Promise<Transport> => {
     return transport;
   } else if (transportType === "sse") {
     const url = query.url as string;
-    const headers: HeadersInit = {
-      Accept: "text/event-stream",
-    };
 
-    for (const key of SSE_HEADERS_PASSTHROUGH) {
-      if (req.headers[key] === undefined) {
-        continue;
-      }
-
-      const value = req.headers[key];
-      headers[key] = Array.isArray(value) ? value[value.length - 1] : value;
-    }
+    const headers = getHttpHeaders(req, transportType);
 
     console.log(`SSE transport: url=${url}, headers=${Object.keys(headers)}`);
 
@@ -104,18 +132,7 @@ const createTransport = async (req: express.Request): Promise<Transport> => {
     await transport.start();
     return transport;
   } else if (transportType === "streamable-http") {
-    const headers: HeadersInit = {
-      Accept: "text/event-stream, application/json",
-    };
-
-    for (const key of STREAMABLE_HTTP_HEADERS_PASSTHROUGH) {
-      if (req.headers[key] === undefined) {
-        continue;
-      }
-
-      const value = req.headers[key];
-      headers[key] = Array.isArray(value) ? value[value.length - 1] : value;
-    }
+    const headers = getHttpHeaders(req, transportType);
 
     const transport = new StreamableHTTPClientTransport(
       new URL(query.url as string),