doc: COSE -> JWK Mappings

**Note**:
- **Browser** WebCrypto only supports **P-256**
- https://caniuse.com/mdn-api_subtlecrypto_sign_ed25519
- **Node** `node:crypto` and WebCrypto also supports **Ed25519** and **secp256k1** (as just `SHA256`) - whatever is supported by openssl v3
- https://nodejs.org/docs/latest/api/webcrypto.html#algorithm-matrix
- https://nodejs.org/docs/latest/api/crypto.html#cryptocreatesignalgorithm-options
- `openssl list -digest-algorithms` (TL;DR: always use `SHA256`)
- `openssl ecparam -list_curves` (`secp256k1`, `prime256v1: X9.62/SECG`, a.k.a `secp256r1` a.k.a. `P-256`)
- `openssl list -public-key-algorithms` (`1.3.101.112, ED25519`, `1.2.840.10045.2.1, EC, id-ecPublicKey`)

#### Node WebCrypto Key Gen Example

```js
'use strict';

let Fs = require('node:fs/promises');

async function generateKeyPair(algo) {
let keyPair = await crypto.subtle.generateKey(algo, true, ['sign', 'verify']);

let privateKeyAb = await crypto.subtle.exportKey('pkcs8', keyPair.privateKey);
let privateKeyDER = new Uint8Array(privateKeyAb);
let privateKeyPath = `./key.${algo.name}.der`.toLowerCase();
await Fs.writeFile(privateKeyPath, privateKeyDER);

let publicKeyAb = await crypto.subtle.exportKey('spki', keyPair.publicKey);
let publicKeyDER = new Uint8Array(publicKeyAb);
let publicKeyPath = `./pub.${algo.name}.der`.toLowerCase();
await Fs.writeFile(publicKeyPath, publicKeyDER);

console.info(`Key pair generated and saved as ${privateKeyPath} and ${publicKeyPath}`);
}

async function main() {
await generateKeyPair({ name: 'Ed25519' });
await generateKeyPair({ name: 'ECDSA', namedCurve: 'P-256' });
}

main().catch(function (err) {
console.error(err.stack);
process.exit(1);
});
```

Adapted From

### OKP (EdDSA / ed25519)

| Key Type | Name | COSE Label | Type | Description | Reference |
| --- | --- | --- | --- | --- | --- |
| 1 | crv | -1 | int / tstr | EC identifier | [RFC9053] |
| 1 | x | -2 | bstr | Public Key | [RFC9053] |
| 1 | d | -4 | bstr | Private key | [RFC9053] |

### EC (ECDSA, secp256k1)

| Key Type | Name | COSE Label | Type | Description | Reference |
| --- | --- | --- | --- | --- | --- |
| 2 | crv | -1 | int / tstr | EC identifier | [RFC9053] |
| 2 | x | -2 | bstr | x-coordinate | [RFC9053] |
| 2 | y | -3 | bstr / bool | y-coordinate | [RFC9053] |

### Modern Keypairs

These are the key types that are still relevant in 2024+ and will be relevant for the next decade:

```js
let coseMap = {
"keys": {
"kty": 1,
"alg": 3
},
"okp": {
"crv": "-1",
"x": "-2",
"d": "-4"
},
"ec": {
"crv": "-1",
"x": "-2",
"y": "-3",
"d": "-4"
},
"kty": {
"1": "OKP",
"2": "EC"
},
"alg": {
"-47": "ES256K",
"-8": "EdDSA",
"-7": "ES256"
},
"crv": {
"1": "P-256",
"6": "Ed25519",
"8": "secp256k1"
}
};
```

### Legacy Keypairs

```js
let coseMap = {
"keys": {
"kty": 1,
"alg": 3
},
"okp": {
"crv": "-1",
"x": "-2",
"d": "-4"
},
"ec": {
"crv": "-1",
"x": "-2",
"y": "-3",
"d": "-4"
},
"rsa": {
"n": "-1",
"e": "-2",
"d": "-3",
"p": "-4",
"q": "-5",
"dp": "-6",
"dq": "-7",
"qi": "-8"
},
"kty": {
"1": "OKP",
"2": "EC",
"3": "RSA"
},
"alg": {
"-259": "RS512",
"-258": "RS384",
"-257": "RS256",
"-39": "PS512",
"-38": "PS384",
"-37": "PS256",
"-36": "ES512",
"-35": "ES384",
"-47": "ES256K",
"-8": "EdDSA",
"-7": "ES256"
},
"crv": {
"1": "P-256",
"2": "P-384",
"3": "P-521",
"6": "Ed25519",
"8": "secp256k1"
}
};
```

### RSA (legacy)

RSA's not bad or broken, it's just not efficient.

| Key Type | Name | COSE Label | Type | Description | Reference |
| --- | --- | --- | --- | --- | --- |
| 3 | n | -1 | bstr | RSA modulus `n` | [RFC8230] |
| 3 | e | -2 | bstr | RSA public exponent `e` | [RFC8230] |
| 3 | d | -3 | bstr | RSA private exponent `d` | [RFC8230] |
| 3 | p | -4 | bstr | Prime factor `p` of `n` | [RFC8230] |
| 3 | q | -5 | bstr | Prime factor `q` of `n` | [RFC8230] |
| 3 | dP | -6 | bstr | `dP` is `d` mod (`p - 1`) | [RFC8230] |
| 3 | dQ | -7 | bstr | `dQ` is `d` mod (`q - 1`) | [RFC8230] |
| 3 | qInv | -8 | bstr | CRT coefficient `q^(-1)` mod `p` | [RFC8230] |
| 3 | other | -9 | array | Other prime infos, an array | [RFC8230] |
| 3 | r_i | -10 | bstr | Prime factor `r_i` of `n`, where `i >= 3` | [RFC8230] |
| 3 | d_i | -11 | bstr | `d_i = d` mod (`r_i - 1`) | [RFC8230] |
| 3 | t_i | -12 | bstr | CRT coefficient `t_i = (r_1 * r_2 * ... * r_(i-1))^(-1)` mod `r_i` | [RFC8230] |

Commencez par examiner les tables de correspondance COSE/JWK et les références IANA, RFC, Node WebCrypto et caniuse liées. Déterminez où la documentation de ce dépôt présente les types de clés passkey, puis documentez les correspondances modernes et héritées convenues avec la prise en charge des navigateurs et de Node. La tâche est terminée lorsque les correspondances et les notes de compatibilité sont complètes et cohérentes en interne.

Rédigé par le modèle d'indexation à partir du texte de l'issue.