refactor: extract common proxyFetch helper in oauth-proxy

Author: asoorm

client/src/lib/oauth-proxy.ts

@@ -17,6 +17,8 @@ import { InspectorConfig } from "./configurationTypes";
 
 /**
  * Get proxy headers for authentication
+ * @param config - Inspector configuration containing proxy authentication settings
+ * @returns Headers object with Content-Type and optional Bearer token
  */
 function getProxyHeaders(config: InspectorConfig): Record<string, string> {
   const { token, header } = getMCPProxyAuthToken(config);
@@ -32,121 +34,147 @@ function getProxyHeaders(config: InspectorConfig): Record<string, string> {
 }
 
 /**
- * Discover OAuth Authorization Server Metadata via proxy
+ * Common helper for proxying fetch requests
+ * @param endpoint - The API endpoint path (e.g., "/oauth/metadata")
+ * @param method - HTTP method (GET or POST)
+ * @param config - Inspector configuration containing proxy settings
+ * @param body - Optional request body object
+ * @param queryParams - Optional query parameters to append to URL
+ * @returns Promise resolving to the typed response
+ * @throws Error if the request fails or returns non-ok status
  */
-export async function discoverAuthorizationServerMetadataViaProxy(
-  authServerUrl: URL,
+async function proxyFetch<T>(
+  endpoint: string,
+  method: "GET" | "POST",
   config: InspectorConfig,
-): Promise<OAuthMetadata> {
+  body?: object,
+  queryParams?: Record<string, string>,
+): Promise<T> {
   const proxyAddress = getMCPProxyAddress(config);
-  const url = new URL("/oauth/metadata", proxyAddress);
-  url.searchParams.set("authServerUrl", authServerUrl.toString());
+  const url = new URL(endpoint, proxyAddress);
+
+  if (queryParams) {
+    Object.entries(queryParams).forEach(([key, value]) => {
+      url.searchParams.set(key, value);
+    });
+  }
 
   const response = await fetch(url.toString(), {
-    method: "GET",
+    method,
     headers: getProxyHeaders(config),
+    ...(body && { body: JSON.stringify(body) }),
   });
 
   if (!response.ok) {
     const error = await response
       .json()
       .catch(() => ({ error: response.statusText }));
-    throw new Error(
-      `Failed to discover OAuth metadata: ${error.error || response.statusText}`,
-    );
+    throw new Error(error.error || response.statusText);
   }
 
   return await response.json();
 }
 
+/**
+ * Discover OAuth Authorization Server Metadata via proxy
+ * @param authServerUrl - The OAuth authorization server URL
+ * @param config - Inspector configuration containing proxy settings
+ * @returns Promise resolving to OAuth metadata
+ * @throws Error if metadata discovery fails
+ */
+export async function discoverAuthorizationServerMetadataViaProxy(
+  authServerUrl: URL,
+  config: InspectorConfig,
+): Promise<OAuthMetadata> {
+  try {
+    return await proxyFetch<OAuthMetadata>(
+      "/oauth/metadata",
+      "GET",
+      config,
+      undefined,
+      { authServerUrl: authServerUrl.toString() },
+    );
+  } catch (error) {
+    throw new Error(
+      `Failed to discover OAuth metadata: ${error instanceof Error ? error.message : String(error)}`,
+    );
+  }
+}
+
 /**
  * Discover OAuth Protected Resource Metadata via proxy
+ * @param serverUrl - The MCP server URL
+ * @param config - Inspector configuration containing proxy settings
+ * @returns Promise resolving to OAuth protected resource metadata
+ * @throws Error if resource metadata discovery fails
  */
 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 }));
+  try {
+    return await proxyFetch<OAuthProtectedResourceMetadata>(
+      "/oauth/resource-metadata",
+      "GET",
+      config,
+      undefined,
+      { serverUrl },
+    );
+  } catch (error) {
     throw new Error(
-      `Failed to discover resource metadata: ${error.error || response.statusText}`,
+      `Failed to discover resource metadata: ${error instanceof Error ? error.message : String(error)}`,
     );
   }
-
-  return await response.json();
 }
 
 /**
  * Register OAuth client via proxy (Dynamic Client Registration)
+ * @param registrationEndpoint - The OAuth client registration endpoint URL
+ * @param clientMetadata - OAuth client metadata for registration
+ * @param config - Inspector configuration containing proxy settings
+ * @returns Promise resolving to OAuth client information
+ * @throws Error if client registration fails
  */
 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 }));
+  try {
+    return await proxyFetch<OAuthClientInformation>(
+      "/oauth/register",
+      "POST",
+      config,
+      { registrationEndpoint, clientMetadata },
+    );
+  } catch (error) {
     throw new Error(
-      `Failed to register client: ${error.error || response.statusText}`,
+      `Failed to register client: ${error instanceof Error ? error.message : String(error)}`,
     );
   }
-
-  return await response.json();
 }
 
 /**
  * Exchange authorization code for tokens via proxy
+ * @param tokenEndpoint - The OAuth token endpoint URL
+ * @param params - Token exchange parameters (code, client_id, etc.)
+ * @param config - Inspector configuration containing proxy settings
+ * @returns Promise resolving to OAuth tokens
+ * @throws Error if token exchange fails
  */
 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({
+  try {
+    return await proxyFetch<OAuthTokens>("/oauth/token", "POST", config, {
       tokenEndpoint,
       params,
-    }),
-  });
-
-  if (!response.ok) {
-    const error = await response
-      .json()
-      .catch(() => ({ error: response.statusText }));
+    });
+  } catch (error) {
     throw new Error(
-      `Failed to exchange authorization code: ${error.error || response.statusText}`,
+      `Failed to exchange authorization code: ${error instanceof Error ? error.message : String(error)}`,
     );
   }
-
-  return await response.json();
 }