confidential-website-metadata-fetcher

README

Confidential Metadata Fetcher

A small service that returns Open Graph metadata and favicons for a URL so Tinfoil Chat can render link preview cards. It runs inside a secure enclave so Tinfoil never sees which links users are previewing.

API

Both POST endpoints take {"url": "..."} and return 400 if the object cannot be decoded or the URL is rejected.

• POST /metadata returns title, description, site_name, image, and the final url after redirects. Missing tags are null. Upstream failures return 502.
• POST /favicon returns status: "found" with base64 favicon_bytes and favicon_content_type, or status: "missing". A temporary upstream failure returns 503 with retryable: true and may set Retry-After; an unusable upstream response returns 502 with retryable: false.
• GET /health returns {"status":"ok"}.

Security

• Only http/https URLs on ports 80 and 443 are accepted; IP literals, embedded credentials, localhost, and hosts ending in .localhost, .local, or .internal are rejected.
• context.dev receives the target URL for metadata (with zero data retention and no shared cache), DuckDuckGo receives only the hostname for favicons, and clients load the image URL directly. Tinfoil sees traffic to those services but not the target URL.
• Responses are sent with Cache-Control: no-store, and nothing is cached in the enclave.
• The service expects a trusted ingress (such as the Tinfoil shim) to authenticate callers; do not expose it directly.

Development

go test ./...
CONTEXT_DEV_API_KEY=your-key go run .

Zero data retention must be enabled for your context.dev organization, otherwise requests fail.

Reporting Vulnerabilities

Please report security vulnerabilities by either:

• Emailing security@tinfoil.sh
• Opening an issue on GitHub on this repository

We aim to respond to (legitimate) security reports within 24 hours.