Added proxy fetch for use by auth (to avoid CORS and other issues when using browser fetch)

client/src/lib/proxyFetch.ts

@@ -0,0 +1,69 @@
+import { getMCPProxyAddress, getMCPProxyAuthToken } from "@/utils/configUtils";
+import type { InspectorConfig } from "./configurationTypes";
+
+interface ProxyFetchResponse {
+  ok: boolean;
+  status: number;
+  statusText: string;
+  headers: Record<string, string>;
+  body: string;
+}
+
+/**
+ * Creates a fetch function that routes requests through the proxy server
+ * to avoid CORS restrictions on OAuth discovery and token endpoints.
+ */
+export function createProxyFetch(config: InspectorConfig): typeof fetch {
+  const proxyAddress = getMCPProxyAddress(config);
+  const { token, header } = getMCPProxyAuthToken(config);
+
+  return async (
+    input: RequestInfo | URL,
+    init?: RequestInit,
+  ): Promise<Response> => {
+    const url = typeof input === "string" ? input : input.toString();
+
+    // Serialize body for JSON transport. URLSearchParams and similar don't
+    // JSON-serialize (they become {}), so we must convert to string first.
+    let serializedBody: string | undefined;
+    if (init?.body != null) {
+      if (typeof init.body === "string") {
+        serializedBody = init.body;
+      } else if (init.body instanceof URLSearchParams) {
+        serializedBody = init.body.toString();
+      } else {
+        serializedBody = String(init.body);
+      }
+    }
+
+    const proxyResponse = await fetch(`${proxyAddress}/fetch`, {
+      method: "POST",
+      headers: {
+        "Content-Type": "application/json",
+        [header]: `Bearer ${token}`,
+      },
+      body: JSON.stringify({
+        url,
+        init: {
+          method: init?.method,
+          headers: init?.headers
+            ? Object.fromEntries(new Headers(init.headers))
+            : undefined,
+          body: serializedBody,
+        },
+      }),
+    });
+
+    if (!proxyResponse.ok) {
+      throw new Error(`Proxy fetch failed: ${proxyResponse.statusText}`);
+    }
+
+    const data: ProxyFetchResponse = await proxyResponse.json();
+
+    return new Response(data.body, {
+      status: data.status,
+      statusText: data.statusText,
+      headers: new Headers(data.headers),
+    });
+  };
+}