API objects

Client Data

The Client Data object is used during user registration, new credential creation, login and action signing

Fido2 credential

When using Fido2, the client data object is built inside the authenticator and returned to the browser base64url encoded. There is no need to modify it.

More information can be found in the W3C webauthn offical specification

field	type	description
type	string	webauthn.create for registration and new credential webauthn.get for login and action signing
challenge	string	The challenge returned from the init call
origin	string	The origin in which the app is being executed
crossOrigin	boolean	A flag indicating if the current call is running cross origin; in most cases this should be false

Example

// Client data as returned by the authenticator during registration
eyJ0eXBlIjoid2ViYXV0aG4uY3JlYXRlIiwiY2hhbGxlbmdlIjoiWTJndE16bGxORFl0YUdKdGRtMHRPR3gwY1hFemMybzBPRGczWlRkd09BIiwib3JpZ2luIjoiaHR0cHM6Ly9hcHAuZGZucy5uaW5qYSIsImNyb3NzT3JpZ2luIjpmYWxzZX0

// Client data object
{
  "type":"webauthn.create",
  "challenge":"Y2gtMzllNDYtaGJtdm0tOGx0cXEzc2o0ODg3ZTdwOA",
  "origin":"https://app.dfns.ninja",
  "crossOrigin":false
}

Key credential

Unlike when using Fido2 credential, the client data object needs to be created manually for Key credential. Once created the object needs to be "stringified" and base64url encoded.

field	type	description
type	string	key.create for registration and new credential key.get for login and action signing
challenge	string	The challenge returned from the init call. The challenge is already base64url encoded, there is no need to encode it
origin	string	The origin in which the app is being executed
crossOrigin	boolean	A flag indicating if the current call is running cross origin; in most cases this should be false

Example

// Client data object
{
  "challenge":"Y2gtNzloaHQtbXJlb2stOGFwOHFtMmVpZWZ0amxhZw",
  "crossOrigin":false,
  "origin":"https://app.dfns.ninja",
  "type":"key.create"
}

// Stringify
'{"challenge":"Y2gtNzloaHQtbXJlb2stOGFwOHFtMmVpZWZ0amxhZw","crossOrigin":false,"origin":"https://app.dfns.ninja","type":"key.create"}'

// Base64url
eyJjaGFsbGVuZ2UiOiJZMmd0Tnpsb2FIUXRiWEpsYjJzdE9HRndPSEZ0TW1WcFpXWjBhbXhoWnciLCJjcm9zc09yaWdpbiI6ZmFsc2UsIm9yaWdpbiI6Imh0dHBzOi8vYXBwLmRmbnMubmluamEiLCJ0eXBlIjoia2V5LmNyZWF0ZSJ9

Attestation Data

This attestation data object is used during registration and new credential.

Fido2 credential

When using Fido2, the attestation data object is built inside the authenticator and returned to the browser. It is encoded using CBOR specification. There is no need to modify it.

More information can be found in the W3C webauthn offical specification.

It is an opaque object and there is no need to describe it here.

Example

// Attestation Data as returned by the authenticator during registration
o2NmbXRmcGFja2VkZ2F0dFN0bXSjY2FsZyZjc2lnWEcwRQIgVHg5PQ_mEyPi_FRZdkgT-SXmspljVaOWJBcN3M0iDxoCIQC8dJkvMWREoJrEdgECSRWzUxXG0WbrpCiajYEJ8mNF5mN4NWOBWQLdMIIC2TCCAcGgAwIBAgIJANVbnGiXosqIMA0GCSqGSIb3DQEBCwUAMC4xLDAqBgNVBAMTI1l1YmljbyBVMkYgUm9vdCBDQSBTZXJpYWwgNDU3MjAwNjMxMCAXDTE0MDgwMTAwMDAwMFoYDzIwNTAwOTA0MDAwMDAwWjBvMQswCQYDVQQGEwJTRTESMBAGA1UECgwJWXViaWNvIEFCMSIwIAYDVQQLDBlBdXRoZW50aWNhdG9yIEF0dGVzdGF0aW9uMSgwJgYDVQQDDB9ZdWJpY28gVTJGIEVFIFNlcmlhbCAxNzU1MDc3NTg5MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEAQap0H_qWf7Lo9-qH8Xj2q-EtN-D_jO0JWxfoyafAdQRcIHIhUMixqtqB9fd5M95L0F4zS7Pvbe5EIA_tns7naOBgTB_MBMGCisGAQQBgsQKDQEEBQQDBQQDMCIGCSsGAQQBgsQKAgQVMS4zLjYuMS40LjEuNDE0ODIuMS43MBMGCysGAQQBguUcAgEBBAQDAgUgMCEGCysGAQQBguUcAQEEBBIEEO6IKHlyHEkTl3U9_M6XByowDAYDVR0TAQH_BAIwADANBgkqhkiG9w0BAQsFAAOCAQEAhDTK-uoXyNUKvzPk-mTjRykakGfJx6CXWJHJAR_zdkHQHaNA-SB8z3a2lmn9sBKI2_-9T3Pasj4gaaXiQxqOXbifp8Iv5nz7rKtmmMuur_u4-XMkOo-wLdZvcjwj-jWdX0daFGmRU0Yck4tYw6-Y_hJ_L8mNT_Odu2jqY3--WlZ8T9H-c9BYhz3dG1MCiQpYH_tw5sz0LXuSFrM3tF_0yEehgtwDwANby9OG7KqUf7O0ArvpBcFFPj8lJf_1_6qXkwFSYxZZzKXHwNsumEdpB7is-X6M4sWG_dcl6msj-hQdtWpxokCWzymdlUG5mk541vtzqpMjM6UvREg1wWjoXmhhdXRoRGF0YVjCtP0s4DAIslfywtetyFg4YfWUmc3GcqHTevk0O6OswibFAAAAAe6IKHlyHEkTl3U9_M6XByoAMEmPqgPRjx312Ywh4gex7TgWLwE2kWRNFGsBomlOLuGIceqoSXgbyAXJgksJs_8_nqUBAgMmIAEhWCBJj6oD0Y8d9dmMIeIHCSUgwKr6FKqaytOhNxEZnGoOYiJYIPGzFTyHoPed-ysej7WwkaaHydkatYmz0rInky2TzyiKoWtjcmVkUHJvdGVjdAI

// CBOR decoded Attestation Data
{
  "authData" : {
    "rpIdHash" : "tP0s4DAIslfywtetyFg4YfWUmc3GcqHTevk0O6OswiY=",
    "flags" : -59,
    "signCount" : 1,
    "attestedCredentialData" : {
      "aaguid" : {
        "value" : "ee882879-721c-4913-9775-3dfcce97072a",
        "bytes" : "7ogoeXIcSROXdT38zpcHKg=="
      },
      "credentialId" : "SY+qA9GPHfXZjCHiB7HtOBYvATaRZE0UawGiaU4u4Yhx6qhJeBvIBcmCSwmz/z+e",
      "cosekey" : {
        "1" : "2",
        "3" : -7,
        "-1" : 1,
        "-2" : "SY+qA9GPHfXZjCHiBwklIMCq+hSqmsrToTcRGZxqDmI=",
        "-3" : "8bMVPIeg9537Kx6PtbCRpofJ2Rq1ibPSsieTLZPPKIo=",
        "1" : 2
      }
    },
    "extensions" : {
      "credProtect" : 2
    },
    "flagUP" : true,
    "flagUV" : true,
    "flagAT" : true,
    "flagED" : true
  },
  "attStmt" : {
    "alg" : -7,
    "sig" : "MEUCIFR4OT0P5hMj4vxUWXZIE/kl5rKZY1WjliQXDdzNIg8aAiEAvHSZLzFkRKCaxHYBAkkVs1MVxtFm66Qomo2BCfJjReY=",
    "x5c" : [ "MIIC2TCCAcGgAwIBAgIJANVbnGiXosqIMA0GCSqGSIb3DQEBCwUAMC4xLDAqBgNVBAMTI1l1YmljbyBVMkYgUm9vdCBDQSBTZXJpYWwgNDU3MjAwNjMxMCAXDTE0MDgwMTAwMDAwMFoYDzIwNTAwOTA0MDAwMDAwWjBvMQswCQYDVQQGEwJTRTESMBAGA1UECgwJWXViaWNvIEFCMSIwIAYDVQQLDBlBdXRoZW50aWNhdG9yIEF0dGVzdGF0aW9uMSgwJgYDVQQDDB9ZdWJpY28gVTJGIEVFIFNlcmlhbCAxNzU1MDc3NTg5MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEAQap0H/qWf7Lo9+qH8Xj2q+EtN+D/jO0JWxfoyafAdQRcIHIhUMixqtqB9fd5M95L0F4zS7Pvbe5EIA/tns7naOBgTB/MBMGCisGAQQBgsQKDQEEBQQDBQQDMCIGCSsGAQQBgsQKAgQVMS4zLjYuMS40LjEuNDE0ODIuMS43MBMGCysGAQQBguUcAgEBBAQDAgUgMCEGCysGAQQBguUcAQEEBBIEEO6IKHlyHEkTl3U9/M6XByowDAYDVR0TAQH/BAIwADANBgkqhkiG9w0BAQsFAAOCAQEAhDTK+uoXyNUKvzPk+mTjRykakGfJx6CXWJHJAR/zdkHQHaNA+SB8z3a2lmn9sBKI2/+9T3Pasj4gaaXiQxqOXbifp8Iv5nz7rKtmmMuur/u4+XMkOo+wLdZvcjwj+jWdX0daFGmRU0Yck4tYw6+Y/hJ/L8mNT/Odu2jqY3++WlZ8T9H+c9BYhz3dG1MCiQpYH/tw5sz0LXuSFrM3tF/0yEehgtwDwANby9OG7KqUf7O0ArvpBcFFPj8lJf/1/6qXkwFSYxZZzKXHwNsumEdpB7is+X6M4sWG/dcl6msj+hQdtWpxokCWzymdlUG5mk541vtzqpMjM6UvREg1wWjoXg" ]
  },
  "fmt" : "packed"
}

Key Credential

Unlike when using Fido2 credential, the attestation data object needs to be created manually for Key credential. Once created the object needs to be "stringified" and base64url encoded.

Before building the attestation data object, the credential info fingerprint object needs to be created.

Credential Info Fingerprint

The attestation data object contains a signature. This section explains how to construct the credential info fingerprint object that is then signed and included in the attestation data object.

Field	Type	Description
clientDataHash	string	The hex encoded SHA-256 hash of the "stringified" client data object
publicKey	string	PEM encoded public key that can be used to verify the signature for the credential

In order for the server to properly verify the signature, the clientDataHash needs to be computed in a reproducible way. That means the "stringified" operation of the client data object needs to be done with the following requirements:

• Keys need to be sorted in alphabetical order: challenge first, then crossOrigin, origin and finally type

• Separators need to be : and , without any space before and after

For example given the following client data object

{
  "challenge":"Y2gtNzloaHQtbXJlb2stOGFwOHFtMmVpZWZ0amxhZw",
  "crossOrigin":false,
  "origin":"https://app.dfns.ninja",
  "type":"key.create"
}

The "stringified" version needs to be

{"challenge":"Y2gtNzloaHQtbXJlb2stOGFwOHFtMmVpZWZ0amxhZw","crossOrigin":false,"origin":"https://app.dfns.ninja","type":"key.create"}

Example

// Client data object
{
  "challenge":"Y2gtNzloaHQtbXJlb2stOGFwOHFtMmVpZWZ0amxhZw",
  "crossOrigin":false,
  "origin":"https://app.dfns.ninja",
  "type":"key.create"
}

// "Stringified" client data
{"challenge":"Y2gtNzloaHQtbXJlb2stOGFwOHFtMmVpZWZ0amxhZw","crossOrigin":false,"origin":"https://app.dfns.ninja","type":"key.create"}

// SHA256 hex encoded
db3828fcdf1782726a7c0c3977679be5fa5a69efa87b295a31b3579a0149edf3

// Credential info fingerprint object
{
  "clientDataHash": "db3828fcdf1782726a7c0c3977679be5fa5a69efa87b295a31b3579a0149edf3",
  "publicKey": "-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE9cG2mE4DWHbwwlLRSKBLZ9m6+QsC\neOqWJh1x5VvRHZMaPLQlRrhhgbHm8una4h8S+L5o8sV8Hvujbl3MrATj3Q==\n-----END PUBLIC KEY-----\n"
}

So the attestation data object is built with the following fields

Field	Type	Description
publicKey	string	PEM encoded public key that can be used to verify the signature for the credential. This the same public key than the one in the Credential Info Fingerprint object
signature	string	The signature produced by signing the "stringified" Credential Info Fingerprint object with the credentials private key, using the algorithm specified in algorithm. Needs to be encoded as a hex string
algorithm	string	Optional The algorithm/digest that the credential will use to sign data. If the algoritm is not specified the algorithm will be determined by the key. Can be one of the following choices: RSA-SHA256 SHA256 SHA512

In order for the server to properly verify the signature, the "stringified" operation of the Credential Info Fingerprint object needs to be done with the following requirements:

• Keys need to be sorted in alphabetical order: clientDataHash first, then publicKey

• Separators need to be : and , without any space before and after

For example given the following client data object

{
  "clientDataHash": "db3828fcdf1782726a7c0c3977679be5fa5a69efa87b295a31b3579a0149edf3",
  "publicKey": "-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE9cG2mE4DWHbwwlLRSKBLZ9m6+QsC\neOqWJh1x5VvRHZMaPLQlRrhhgbHm8una4h8S+L5o8sV8Hvujbl3MrATj3Q==\n-----END PUBLIC KEY-----\n"
}

The "stringified" version needs to be

{"clientDataHash":"db3828fcdf1782726a7c0c3977679be5fa5a69efa87b295a31b3579a0149edf3","publicKey":"-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE9cG2mE4DWHbwwlLRSKBLZ9m6+QsC\neOqWJh1x5VvRHZMaPLQlRrhhgbHm8una4h8S+L5o8sV8Hvujbl3MrATj3Q==\n-----END PUBLIC KEY-----\n"}

The signature also needs to be generated with pre-defined hash algorithm and encoding:

• Hash algorithm: SHA256

• Encoding: DER. See Signature Format for more information

Signing Example

keyOrPasswordClientData: {
  type: 'key.create',
  challenge: challenge,
  origin: this.appOrigin,
  crossOrigin: false,
}

const clientData = Buffer.from(JSON.stringify(supportedCredentials.credentialData.keyOrPasswordClientData))
const signaturePayload = Buffer.from(JSON.stringify({
  clientDataHash: crypto.createHash('sha256').update(clientData).digest('hex'),
  publicKey: newKey.publicKey,
}))
const signature = crypto.sign(undefined, signaturePayload, newKey.privateKey)

Example

// Hex encoded signature of the string '{"clientDataHash":"db3828fcdf1782726a7c0c3977679be5fa5a69efa87b295a31b3579a0149edf3","publicKey":"-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE9cG2mE4DWHbwwlLRSKBLZ9m6+QsC\neOqWJh1x5VvRHZMaPLQlRrhhgbHm8una4h8S+L5o8sV8Hvujbl3MrATj3Q==\n-----END PUBLIC KEY-----\n"}'
30460221008e0109848c6fc83004d0e6c7fdac71dae8524fc5a29081d012f865416986ce29022100f47e1bee6c5175c4488b143c936c68fac1ae7e7931e76c677d46331ed149d17d

// Attestation Data object
{
  "publicKey": "-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE9cG2mE4DWHbwwlLRSKBLZ9m6+QsC\neOqWJh1x5VvRHZMaPLQlRrhhgbHm8una4h8S+L5o8sV8Hvujbl3MrATj3Q==\n-----END PUBLIC KEY-----\n",
  "signature": "30460221008e0109848c6fc83004d0e6c7fdac71dae8524fc5a29081d012f865416986ce29022100f47e1bee6c5175c4488b143c936c68fac1ae7e7931e76c677d46331ed149d17d"
}

// Stringify
'{"publicKey": "-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE9cG2mE4DWHbwwlLRSKBLZ9m6+QsC\neOqWJh1x5VvRHZMaPLQlRrhhgbHm8una4h8S+L5o8sV8Hvujbl3MrATj3Q==\n-----END PUBLIC KEY-----\n","signature":"30460221008e0109848c6fc83004d0e6c7fdac71dae8524fc5a29081d012f865416986ce29022100f47e1bee6c5175c4488b143c936c68fac1ae7e7931e76c677d46331ed149d17d"}'

// Base64url
eyJwdWJsaWNLZXkiOiAiLS0tLS1CRUdJTiBQVUJMSUMgS0VZLS0tLS1cbk1Ga3dFd1lIS29aSXpqMENBUVlJS29aSXpqMERBUWNEUWdBRTljRzJtRTREV0hid3dsTFJTS0JMWjltNitRc0NcbmVPcVdKaDF4NVZ2UkhaTWFQTFFsUnJoaGdiSG04dW5hNGg4UytMNW84c1Y4SHZ1amJsM01yQVRqM1E9PVxuLS0tLS1FTkQgUFVCTElDIEtFWS0tLS0tXG4iLCJzaWduYXR1cmUiOiIzMDQ2MDIyMTAwOGUwMTA5ODQ4YzZmYzgzMDA0ZDBlNmM3ZmRhYzcxZGFlODUyNGZjNWEyOTA4MWQwMTJmODY1NDE2OTg2Y2UyOTAyMjEwMGY0N2UxYmVlNmM1MTc1YzQ0ODhiMTQzYzkzNmM2OGZhYzFhZTdlNzkzMWU3NmM2NzdkNDYzMzFlZDE0OWQxN2QifQ