# `Attesto.CredentialOfferStore`
[🔗](https://github.com/XukuLLC/attesto/blob/v2.0.1/lib/attesto/credential_offer_store.ex#L1)

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.

# `entry`

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

# `fetch`

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

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

# `put`

```elixir
@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.

---

*Consult [api-reference.md](api-reference.md) for complete listing*