implemented a standalone DiscoveryDocumentCache utility class to help users reduce unnecessary network requests when fetching OAuth/OpenID Connect discovery documents during authentication:

• TTL-based caching: configurable time-to-live (default: 1 hour)
• promise coalescing: prevents duplicate fetches for concurrent requests to the same URL
• proper timing: TTL calculated after fetch completes, not before
• cache invalidation: support for clearing specific URLs or entire cache
• simple API: just call cache.get(url) and it handles the rest

example:

import { FastMCP, DiscoveryDocumentCache } from "fastmcp";

// Create cache instance (reuse across requests)
const discoveryCache = new DiscoveryDocumentCache({
  ttl: 3600000, // 1 hour (default)
});

const mcp = new FastMCP("My Server");

// Use in authenticate handler
mcp.authenticate(async ({ sessionId }) => {
  const config = await discoveryCache.get('https://auth.example.com/.well-known/openid-configuration');
  const jwksUri = config.jwks_uri;
  // ... //
});

addresses the TODO in docs about caching discovery documents.