feat: add OAuth proxy utility functions

- Create discoverAuthorizationServerMetadataViaProxy()
- Create discoverOAuthProtectedResourceMetadataViaProxy()
- Create registerClientViaProxy() for DCR
- Create exchangeAuthorizationViaProxy() for token exchange
- Reuse getMCPProxyAddress() and getMCPProxyAuthToken() for consistency
- Provide clear error messages for debugging

Author: asoorm

client/src/lib/oauth-proxy.ts

@@ -0,0 +1,152 @@
+/**
+ * OAuth Proxy Utilities
+ *
+ * These functions route OAuth requests through the MCP Inspector proxy server
+ * to avoid CORS issues when connectionType is "proxy".
+ */
+
+import {
+  OAuthMetadata,
+  OAuthProtectedResourceMetadata,
+  OAuthClientInformation,
+  OAuthTokens,
+  OAuthClientMetadata,
+} from "@modelcontextprotocol/sdk/shared/auth.js";
+import { getMCPProxyAddress, getMCPProxyAuthToken } from "@/utils/configUtils";
+import { InspectorConfig } from "./configurationTypes";
+
+/**
+ * Get proxy headers for authentication
+ */
+function getProxyHeaders(config: InspectorConfig): Record<string, string> {
+  const { token, header } = getMCPProxyAuthToken(config);
+  const headers: Record<string, string> = {
+    "Content-Type": "application/json",
+  };
+
+  if (token) {
+    headers[header] = `Bearer ${token}`;
+  }
+
+  return headers;
+}
+
+/**
+ * Discover OAuth Authorization Server Metadata via proxy
+ */
+export async function discoverAuthorizationServerMetadataViaProxy(
+  authServerUrl: URL,
+  config: InspectorConfig,
+): Promise<OAuthMetadata> {
+  const proxyAddress = getMCPProxyAddress(config);
+  const url = new URL("/oauth/metadata", proxyAddress);
+  url.searchParams.set("authServerUrl", authServerUrl.toString());
+
+  const response = await fetch(url.toString(), {
+    method: "GET",
+    headers: getProxyHeaders(config),
+  });
+
+  if (!response.ok) {
+    const error = await response
+      .json()
+      .catch(() => ({ error: response.statusText }));
+    throw new Error(
+      `Failed to discover OAuth metadata: ${error.error || response.statusText}`,
+    );
+  }
+
+  return await response.json();
+}
+
+/**
+ * Discover OAuth Protected Resource Metadata via proxy
+ */
+export async function discoverOAuthProtectedResourceMetadataViaProxy(
+  serverUrl: string,
+  config: InspectorConfig,
+): Promise<OAuthProtectedResourceMetadata> {
+  const proxyAddress = getMCPProxyAddress(config);
+  const url = new URL("/oauth/resource-metadata", proxyAddress);
+  url.searchParams.set("serverUrl", serverUrl);
+
+  const response = await fetch(url.toString(), {
+    method: "GET",
+    headers: getProxyHeaders(config),
+  });
+
+  if (!response.ok) {
+    const error = await response
+      .json()
+      .catch(() => ({ error: response.statusText }));
+    throw new Error(
+      `Failed to discover resource metadata: ${error.error || response.statusText}`,
+    );
+  }
+
+  return await response.json();
+}
+
+/**
+ * Register OAuth client via proxy (Dynamic Client Registration)
+ */
+export async function registerClientViaProxy(
+  registrationEndpoint: string,
+  clientMetadata: OAuthClientMetadata,
+  config: InspectorConfig,
+): Promise<OAuthClientInformation> {
+  const proxyAddress = getMCPProxyAddress(config);
+  const url = new URL("/oauth/register", proxyAddress);
+
+  const response = await fetch(url.toString(), {
+    method: "POST",
+    headers: getProxyHeaders(config),
+    body: JSON.stringify({
+      registrationEndpoint,
+      clientMetadata,
+    }),
+  });
+
+  if (!response.ok) {
+    const error = await response
+      .json()
+      .catch(() => ({ error: response.statusText }));
+    throw new Error(
+      `Failed to register client: ${error.error || response.statusText}`,
+    );
+  }
+
+  return await response.json();
+}
+
+/**
+ * Exchange authorization code for tokens via proxy
+ */
+export async function exchangeAuthorizationViaProxy(
+  tokenEndpoint: string,
+  params: Record<string, string>,
+  config: InspectorConfig,
+): Promise<OAuthTokens> {
+  const proxyAddress = getMCPProxyAddress(config);
+  const url = new URL("/oauth/token", proxyAddress);
+
+  const response = await fetch(url.toString(), {
+    method: "POST",
+    headers: getProxyHeaders(config),
+    body: JSON.stringify({
+      tokenEndpoint,
+      params,
+    }),
+  });
+
+  if (!response.ok) {
+    const error = await response
+      .json()
+      .catch(() => ({ error: response.statusText }));
+    throw new Error(
+      `Failed to exchange authorization code: ${error.error || response.statusText}`,
+    );
+  }
+
+  return await response.json();
+}