@sylphx/pdf-reader-mcp: HTTP transport accepts unauthenticated requests despite a configured MCP_API_KEY

### Impact When `@sylphx/pdf-reader-mcp` is run as an HTTP server (`MCP_TRANSPORT=http`), it reads the `MCP_API_KEY` environment variable and logs `API key authentication enabled (X-API-Key header)` at startup, but it never validated the `X-API-Key` header on incoming requests. The key was read into a variable and never enforced on the request path. As a result, the `/mcp` endpoint accepted **unauthenticated** requests. Combined with the default bind address of `0.0.0.0` (all interfaces), any client able to reach the port could invoke every PDF tool and read the contents of any PDF the server process could open anywhere on the host. URL-based sources also enable limited SSRF (private/loopback addresses are blocked by default unless `--allow-private-ips` is set). The misleading startup log made the exposure silent: an operator who set `MCP_API_KEY` reasonably believed the server was protected when it was not. This affects only the opt-in HTTP transport; the default `stdio` transport is unaffected. ### Patches Fixed in `@sylphx/pdf-reader-mcp@3.0.1`. The fix enforces the `X-API-Key` header with a constant-time comparison (rejecting missing/mismatched keys with HTTP 401), changes the default bind host to `127.0.0.1` (loopback), and emits a startup warning when binding a non-loopback host without an API key. ### Workarounds For deployments that cannot upgrade immediately: - Bind to loopback only: `MCP_HTTP_HOST=127.0.0.1`. - Place a reverse proxy in front that enforces authentication. - Use the default `stdio` transport instead of HTTP. - Restrict filesystem reach with `--allow-dir` / `MCP_PDF_ALLOWED_DIRS`. Reported privately by **novice-22** via responsible disclosure.