Download the passport Verifiable Credential

Returns the signed W3C Verifiable Credential (UNTP Digital Product Passport) as JSON-LD, served from the copy persisted at certification (also pinned to IPFS, which is read back as fallback) — or, for a self-hosted certificate, read on the fly from the issuer-provided certificateUri (never stored server-side). Public: a third-party verifier resolves the issuer did:web and checks the signature without contacting Keyban. Returns 404 when the passport is not visible to the caller (anonymously it must be published or claimed), and 200 with an unsigned minimal credential while it is not certified yet. Returns 503 when no persisted copy exists and the IPFS gateway is unreachable, or when the self-hosted certificate cannot be retrieved (e.g. deleted by the issuer). CORS-open for browser verifiers.