Attesto.CredentialOfferStore behaviour (Attesto v1.10.0)

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Storage seam for by-reference OID4VCI credential offers.

An issuer stores a credential offer under an opaque id and gives the wallet a URI containing that id. The wallet retrieves the offer through fetch/1. Retrieval is non-consuming: the pre-authorized code inside the offer is the single-use gate for the issuance flow.

The id is a capability — do not choose it yourself

The offer endpoint is unauthenticated (the wallet dereferences the credential_offer_uri before it holds any token), and a pre-authorized offer embeds a redeemable pre-authorized_code. The id is the ONLY thing standing between an attacker and that code: a guessable id lets them enumerate the endpoint and redeem a victim's offer. Create offers through Attesto.CredentialOffer.store_by_reference/3, which generates a 256-bit CSPRNG id and calls put/1 for you. Never call put/1 with a self-chosen or low-entropy id.

Summary

Types

entry()

Callbacks

fetch(id)

Fetch a live offer without consuming it, or return :error.

put(entry)

Persist a credential-offer record.

Types

entry()

@type entry() :: %{id: String.t(), offer: map(), expires_at: integer()}

Callbacks

fetch(id)

@callback fetch(id :: String.t()) :: {:ok, map()} | :error

Fetch a live offer without consuming it, or return :error.

put(entry)

@callback put(entry()) :: :ok

Persist a credential-offer record.

The :id MUST be an unguessable, high-entropy value. Use Attesto.CredentialOffer.store_by_reference/3 rather than calling this directly — it generates the id so a weak one can't slip in.