JSON helpers for WebAuthn

A set of functions for converting to and from JSON compatible structures, useful for passing these values between clients and servers as JSON strings.

Example

import {
  parseCreationOptionsFromJSON,
  attestationToJSON,
} from 'https://esm.sh/gh/tjconcept/webauthn-json@1.1.0'

function signUp() {
  const credential = navigator.credentials.create({
    publicKey: parseCreationOptionsFromJSON(JSON.parse(serverWebauthnCreate())),
  })
  join(credential, (credential) =>
    serverWebauthnStore(JSON.stringify(attestationToJSON(credential))),
  )
}

Exports

creationOptionsToJSON(options) → json
parseCreationOptionsFromJSON(json) → options
requestOptionsToJSON(options) → json
parseRequestOptionsFromJSON(json) → options
assertionToJSON(credential) → json
assertionFromJSON(json) → credential
attestationToJSON(credential) → json
attestationFromJSON(json) → credential
pubKeyCredParams = [
  {alg: -8, type: 'public-key'},   // EdDSA
  {alg: -7, type: 'public-key'},   // ES256
  {alg: -257, type: 'public-key'}, // RS256
]

pubKeyCredParams

A convenient list of common algorithms that can be filtered or sorted to specific needs.

Example

const supported = [-8, -257]
navigator.credentials.create({
  publicKey: {
    authenticatorSelection: {residentKey: true},
    challenge: Uint8Array.from([1, 2, 3, 4]),
    pubKeyCredParams: pubKeyCredParams.filter((p) => supported.includes(p.alg)),
    rp: 'example.com',
    user: {
      name: 'Foo',
      displayName: 'Bar',
      id: Uint8Array.from([5, 6, 7, 8]),
    },
  },
})

parseCreationOptionsFromJSON(json)

Ponyfill of PublicKeyCredential.parseCreationOptionsFromJSON().

Decode Base64-URL strings in challenge and user.id to Uint8Array values.

Example

navigator.credentials.create({
  publicKey: parseCreationOptionsFromJSON(JSON.parse(serverResponse)),
})

creationOptionsToJSON(options)

Partner (reverse) of PublicKeyCredential.parseCreationOptionsFromJSON().

Encode ArrayBuffer or Uint8Array values in challenge and user.id as Base64-URL strings.

Example

const serverResponse = creationOptionsToJSON({
  authenticatorSelection: {residentKey: true},
  challenge: Uint8Array.from([1, 2, 3, 4]),
  pubKeyCredParams: [{alg: -8, type: 'public-key'}],
  rp: 'example.com',
  user: {
    name: 'Foo',
    displayName: 'Bar',
    id: Uint8Array.from([5, 6, 7, 8]),
  },
})
sendToClient(JSON.stringify(serverResponse))

parseRequestOptionsFromJSON(json)

Ponyfill of PublicKeyCredential.parseRequestOptionsFromJSON().

Decode Base64-URL strings in challenge and allowCredentials[].id to Uint8Array values.

Example

navigator.credentials.get({
  publicKey: parseRequestOptionsFromJSON(JSON.parse(serverResponse)),
})

requestOptionsToJSON(options)

Partner (reverse) of PublicKeyCredential.parseRequestOptionsFromJSON().

Encode ArrayBuffer or Uint8Array values in challenge and allowCredentials[].id as Base64-URL strings.

Example

const serverResponse = creationOptionsToJSON({
  allowCredentials: [
    {
      id: Uint8Array.from([5, 6, 7, 8]),
      transports: ['ble', 'nfc'],
      type: 'public-key',
    },
  ],
  challenge: Uint8Array.from([1, 2, 3, 4]),
  extensions: {
    foo: 'bar',
  },
  hints: ['hybrid'],
  rpId: 'example.com',
  timeout: 12000,
  userVerification: 'preferred',
})
sendToClient(JSON.stringify(serverResponse))

assertionToJSON(credential)

Encode ArrayBuffer or Uint8Array values in the following paths as Base64-URL strings:

• rawId
• response.authenticatorData
• response.clientDataJSON
• response.signature
• response.userHandle

Example

navigator.credentials
  .get({
    publicKey: parseRequestOptionsFromJSON(JSON.parse(serverResponse)),
  })
  .then((credential) =>
    sendToServer(JSON.stringify(assertionToJSON(credential))),
  )

assertionFromJSON(json)

Decode Base64-URL strings in the following paths to Uint8Array values:

• rawId
• response.authenticatorData
• response.clientDataJSON
• response.signature
• response.userHandle

Example

const assertion = assertionFromJSON(JSON.parse(clientResponse))
// assertion.response.signature

attestationToJSON(credential)

Encode ArrayBuffer or Uint8Array values as Base64-URL strings and replace "getter" functions with their result:

• rawId is Base64-URL encoded
• response.attestationObject is Base64-URL encoded
• response.clientDataJSON is Base64-URL encoded
• response.authenticatorData is the Base64-URL encoded result from response.getAuthenticatorData()
• response.publicKey is the Base64-URL encoded result from response.getPublicKey()
• response.publicKeyAlgorithm is the result from response.getPublicKeyAlgorithm()
• response.transports is the result from response.getTransports()

Example

navigator.credentials
  .create({
    publicKey: parseCreationOptionsFromJSON(JSON.parse(serverResponse)),
  })
  .then((credential) => sendToServer(attestationToJSON(credential)))

attestationFromJSON(json)

Decode Base64-URL strings in the following paths to Uint8Array values:

• rawId
• response.attestationObject
• response.clientDataJSON
• response.authenticatorData
• response.publicKey

Note that this function is not an exact mirroring of attestationToJSON(PublicKeyCredential) as it will not reproduce the "getter" functions but replace them with a corresponding key-value pair, e.g. getAuthenticatorData: () → String is replaced by authenticatorData: String. However, it is a mirroring of attestationToJSON(json), such that attestationToJSON(attestationFromJSON(json)) will work. This simply means it works as expected and can be used on both ends to transfer or store attestations (e.g. using JSON.stringify/parse).

Example

const attestation = attestationFromJSON(JSON.parse(clientResponse))
if (attestation.response.publicKeyAlgorithm !== -8) {
  throw new Error('Algorithm not supported')
}

const key = crypto.subtle.importKey(
  'spki',
  attestation.response.publicKey,
  {name: 'Ed25519'},
  extractable,
  usages,
)

Testing

deno --allow-env --allow-read test.js