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* Copyright (c) 2026 The Triauth Authors (https://www.triauth.org/)
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* SPDX-License-Identifier: Apache-2.0
*/
import { Base } from './base.js';
import { register } from './registry.js';
import { Helpers } from '../helpers.js';
/**
* The base abstract verifier for WebAuthn signatures.
*
* Performs the WebAuthn-level assertion validation.
* Subclasses must define concrete importAlgorithm, verifyAlgorithm, and register themselves (e.g., as `webauthn-es256`).
*
* @class
* @memberof Triauth.Verifiers
*/
export class WebAuthn extends Base {
// The Web Crypto parameters used to import the publishable key and to verify
// assertion signatures. Concrete subclasses MUST override these to bind a
// credential algorithm; left null, the verifier fails closed.
/** @type {AlgorithmIdentifier | RsaHashedImportParams | EcKeyImportParams | HmacImportParams | AesKeyAlgorithm | null} */
static importAlgorithm = null;
/** @type {AlgorithmIdentifier | RsaPssParams | EcdsaParams | null} */
static verifyAlgorithm = null;
/**
* Constructs a new instance of verifier for the given public crypto key and options.
*
* @param publicKey {CryptoKey} - A public key in form of CryptoKey object.
* @param [options={}] {object} - Key options as read from the DNS record that contained the publicKey.
* Supports `uv: 'required'` - assertions are then accepted only with the User Verified (UV) flag set
* (i.e., the authenticator checked PIN/biometrics).
* @param [context={}] {{idx?: number, mode?: string, webAuthnOrigin?: string}} -
* Per-verification context. `idx` (key's index in its keyGroup) selects which `unsignedData.sig[idx]` entry to verify against;
* `webAuthnOrigin`, if set, is enforced against `clientData.origin`. Stored on `this.context`.
* @param [config={}] {object} - Optional overrides for the global Triauth.config settings
*/
constructor(publicKey, options = {}, context = {}, config = {}) {
super();
this.publicKey = publicKey;
this.options = options;
this.context = context;
this.config = Helpers.mergeConfig(config);
}
/**
* Builds an instance of the Verifier from the raw key information read from the DNS.
*
* @param rawPublicKey {string} - A key as published in the DNS record.
* @param [options={}] {object} - Key options as read from the DNS record that contained the rawPublicKey.
* @param [context={}] {{idx?: number, mode?: string, webAuthnOrigin?: string}} -
* Per-verification context. `idx` (key's index in its keyGroup) selects which `unsignedData.sig[idx]` entry to verify against;
* `webAuthnOrigin`, if set, is enforced against `clientData.origin`. Stored on `this.context`.
* @param [config={}] {object} - Optional overrides for the global Triauth.config settings
*
* @returns {Promise<WebAuthn|null>} A promise that resolves to the instance of this verifier, or null if key is invalid or other problem occurred.
*/
static async fromPublishableKey(rawPublicKey, options = {}, context = {}, config = {}) {
config = Helpers.mergeConfig(config);
const importAlgorithm = this.importAlgorithm;
if (!importAlgorithm) {
config.logger?.debug?.('WebAuthn is an algorithm-agnostic base verifier - use a concrete subclass (e.g., WebAuthnEs256)');
return null;
}
try {
const publicKey = (await crypto.subtle.importKey('raw', /** @type {BufferSource} */ (Helpers.base64UrlToUint8(rawPublicKey)), importAlgorithm, true, ['verify']));
return new this(publicKey, options, context, config);
} catch (err) {
config.logger?.debug?.(err);
return null;
}
}
/**
* Verifies that a given signature matches the verifier's public key and the given message.
*
* @param message {string} - The message that was signed; its SHA-256 digest must match `clientData.challenge`.
* @param signatureBase64Url {string} - Base64Url encoded signature over `(authenticatorData || sha256(clientDataJSON))`.
* @param signedData {object} - Signature envelope's signedMetadata. Unused by this verifier.
* @param unsignedData {{sig: Object<number, {clientDataJSON: string, authenticatorData: string}>}} -
* Signature envelope's unsignedMetadata. Must contain `sig[idx]` for this key's index (set on `this.context.idx`),
* carrying the original `clientDataJSON` (string) and `authenticatorData` (base64url, minimum 37 bytes,
* with the User Present flag set - silent CTAP-level assertions are rejected).
*
* @returns {Promise<boolean>} A promise that resolves to true or false basing on the verification result.
*/
async verify(message, signatureBase64Url, signedData, unsignedData) {
try {
/** @type {AlgorithmIdentifier | RsaPssParams | EcdsaParams | null} */
const verifyAlgorithm = (/** @type {*} */ (this.constructor)).verifyAlgorithm;
if (!verifyAlgorithm) {
this.config.logger?.debug?.('WebAuthn is an algorithm-agnostic base verifier - use a concrete subclass (e.g., WebAuthnEs256)');
return false;
}
const idx = this.context.idx;
const expectedChallenge = await Helpers.sha256(message);
const expectedOrigin = this.context.webAuthnOrigin;
// SECURITY NOTE: `unsignedData` is NOT covered by the triauth envelope's signature, but:
// - clientData.challenge is checked to be the expectedChallenge
// - (authenticatorData + sha256(clientDataJSON)) is covered by the WebAuthn-signed payload
if (
typeof unsignedData !== 'object' ||
typeof unsignedData.sig !== 'object' ||
typeof unsignedData.sig[idx] !== 'object' ||
typeof unsignedData.sig[idx].clientDataJSON !== 'string' ||
!Helpers.isBase64UrlString(unsignedData.sig[idx].authenticatorData)
) {
return false;
}
const { authenticatorData, clientDataJSON } = unsignedData.sig[idx];
// Verify clientData structure, including that the clientData.challenge is an SHA-256 digest of the message
const clientData = Helpers.safeParseJson(clientDataJSON);
if(
clientData.challenge !== expectedChallenge || // <--- challenge MUST MATCH --- !!!
clientDataJSON.match(/"challenge":/g).length !== 1 || // Ensure that "challenge" key appears exactly once in the clientDataJSON, as an extra safety precaution
clientData.type !== 'webauthn.get' || // type should always be 'webauthn.get'
(clientData.crossOrigin !== false && clientData.crossOrigin !== undefined) || // if present, must be exactly false (a cross-origin <iframe> assertion carries true); the member is optional and absent means top-level same-origin (WebKit omits it)
(expectedOrigin && clientData.origin !== expectedOrigin) // origin, if available from context, must match
) {
return false;
}
// Parse the authenticatorData: 32-byte rpIdHash, 1 flags byte, 4-byte signCount (37 bytes minimum)
const authenticatorDataBytes = Helpers.base64UrlToUint8(authenticatorData);
if (authenticatorDataBytes.length < 37) {
this.config.logger?.debug?.('WebAuthn assertion rejected - authenticatorData shorter than 37 bytes');
return false;
}
// Require the User Present (UP) flag, as the W3C Web Authentication specification mandates for assertions.
// Browser-mediated assertions always carry UP=1 (the client performs a presence test before
// returning one); its absence indicates a CTAP-level "silent" assertion (options.up=false),
// e.g., minted by malware with direct access to a connected authenticator.
//
// The rpIdHash (bytes 0-31) is intentionally NOT checked: the public key is pinned in the
// DNS identity records and a WebAuthn credential only ever signs under its own rpId, so
// there is no cross-RP credential confusion to prevent; the phishing angle is covered by
// the clientData.origin check above. The signCount (bytes 33-36) is not checked either:
// clone detection requires server-side state that this stateless verifier does not have
// (and modern passkeys report a constant 0).
if ((authenticatorDataBytes[32] & 0x01) !== 0x01) {
this.config.logger?.debug?.('WebAuthn assertion rejected - User Present (UP) flag not set');
return false;
}
// When the key record demands user verification (`uv=required`), also require the
// User Verified (UV) flag - i.e., the authenticator must have checked PIN/biometrics.
// Key records carrying any other `uv` value never reach this point - they taint their
// whole keyGroup during Triauth.IdentityKeys#add (fail closed, never silently weaker).
if (this.options.uv === 'required' && (authenticatorDataBytes[32] & 0x04) !== 0x04) {
this.config.logger?.debug?.('WebAuthn assertion rejected - User Verified (UV) flag required by key options but not set');
return false;
}
// Reconstruct the payload that was signed by webauthn
const clientDataHash = await crypto.subtle.digest(
'SHA-256',
/** @type {BufferSource} */ (Helpers.stringToUtf8Bytes(clientDataJSON))
);
const webAuthnPayload = new Uint8Array([
...new Uint8Array(authenticatorDataBytes),
...new Uint8Array(clientDataHash)
]);
// Convert the signature being verified back to UInt8Array for crypto.verify
const signature = Helpers.base64UrlToUint8(signatureBase64Url);
// Verify the digital signature (may raise an exception if arguments are invalid)
return await crypto.subtle.verify(
verifyAlgorithm,
this.publicKey,
/** @type {BufferSource} */ (signature),
webAuthnPayload
);
} catch (err) {
this.config.logger?.debug?.(err);
return false;
}
}
}
/**
* A verifier for WebAuthn signatures backed by ECDSA P-256 (ES256) credentials.
*
* Shares all WebAuthn assertion validation with the WebAuthn base class; this subclass
* only binds the ES256 credential algorithm.
*
* @class
* @memberof Triauth.Verifiers
*
*/
export class WebAuthnEs256 extends WebAuthn {
static importAlgorithm = { name: 'ECDSA', namedCurve: 'P-256', hash: 'SHA-256' };
static verifyAlgorithm = { name: 'ECDSA', hash: 'SHA-256' };
}
/**
* A verifier for WebAuthn signatures backed by Ed25519 (EdDSA over Curve25519) credentials.
*
* Shares all WebAuthn assertion validation with the WebAuthn base class; this subclass
* only binds the Ed25519 credential algorithm. Like the plain Ed25519 verifier, it requires
* Ed25519 support in the runtime's Web Crypto API (Node.js 18.4+; Safari 17+, Firefox 130+,
* Chrome/Edge 137+) - on runtimes without it, `fromPublishableKey` resolves to null and the
* keyGroup fails verification (fail closed).
*
* @class
* @memberof Triauth.Verifiers
*
*/
export class WebAuthnEd25519 extends WebAuthn {
static importAlgorithm = { name: 'Ed25519' };
static verifyAlgorithm = { name: 'Ed25519' };
}
register('webauthn-es256', WebAuthnEs256);
register('webauthn-ed25519', WebAuthnEd25519);
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