Add Accept header to auth metadata request

Author: SVLaursen

src/client/auth.ts

@@ -750,7 +750,10 @@ export async function discoverAuthorizationServerMetadata(
     protocolVersion?: string;
   } = {}
 ): Promise<AuthorizationServerMetadata | undefined> {
-  const headers = { 'MCP-Protocol-Version': protocolVersion };
+  const headers = { 
+    'MCP-Protocol-Version': protocolVersion,
+    'Accept': 'application/json', 
+  };
 
   // Get the list of URLs to try
   const urlsToTry = buildDiscoveryUrls(authorizationServerUrl);