# `Hmac`

An HMAC-SHA-256 tag (RFC 2104): the 32 bytes `crypto.hmac` gives, a webhook's signature among them. Compared in constant time.

[Security](types.md#security); not ordered; since Jadpo 0.1.0.

## Make one

Build one from `Bytes`, `Hmac(bytes)`, which checks them: bytes that aren't one break `format`.

`text.parse(raw, as: Hmac)` reads one from its text; text that isn't one at all fails `malformed`, such as `""`.

## Text, JSON and storage

`text.from` writes its canonical text, the one form `text.parse` reads back. JSON sends its canonical text as a string.

| Text | JSON |
|---|---|
| `sDRMYdjbOFNcqK/OrwvxK4gdwgDJgz2nJuk3bC4yz/c=` | `"sDRMYdjbOFNcqK/OrwvxK4gdwgDJgz2nJuk3bC4yz/c="` |
| `W9zBRr9gdU5qBCQmCJV1x1oAPwidJzmDnexYuWTsOEM=` | `"W9zBRr9gdU5qBCQmCJV1x1oAPwidJzmDnexYuWTsOEM="` |

It is stored in one column named for the field, of type `bytea`. `W9zBRr9gdU5qBCQmCJV1x1oAPwidJzmDnexYuWTsOEM=` is stored as `E'\\x5bdcc146bf60754e6a042426089575c75a003f089d2739839dec58b964ec3843'::bytea`.

## Shown to people

`text.format(value, locale:)` shows it to people in their locale.

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `sDRMYdjbOFNcqK/OrwvxK4gdwgDJgz2nJuk3bC4yz/c=` | `sDRMYdjbOFNcqK/OrwvxK4gdwgDJgz2nJuk3bC4yz/c=` |
| `W9zBRr9gdU5qBCQmCJV1x1oAPwidJzmDnexYuWTsOEM=` | `W9zBRr9gdU5qBCQmCJV1x1oAPwidJzmDnexYuWTsOEM=` |

## Operations

It has the contract's own operations: `text.parse`, `text.from`, `text.format`, `json.read`, `json.write` and `==`. It isn't ordered, so `<` and sorting don't take it. [Every standard type meets one contract](../topics/every-standard-type-meets-one-contract.md) says how they work.