1 files changed, 66 insertions, 0 deletions
diff --git a/packages/browser/src/methods/startAuthentication.ts b/packages/browser/src/methods/startAuthentication.ts
new file mode 100644
index 0000000..277b8f0
--- /dev/null
+++ b/packages/browser/src/methods/startAuthentication.ts
@@ -0,0 +1,66 @@
+import {
+  PublicKeyCredentialRequestOptionsJSON,
+  AuthenticationCredential,
+  AuthenticationCredentialJSON,
+} from '@simplewebauthn/typescript-types';
+
+import bufferToBase64URLString from '../helpers/bufferToBase64URLString';
+import base64URLStringToBuffer from '../helpers/base64URLStringToBuffer';
+import bufferToUTF8String from '../helpers/bufferToUTF8String';
+import { browserSupportsWebauthn } from '../helpers/browserSupportsWebauthn';
+import toPublicKeyCredentialDescriptor from '../helpers/toPublicKeyCredentialDescriptor';
+
+/**
+ * Begin authenticator "login" via WebAuthn assertion
+ *
+ * @param requestOptionsJSON Output from @simplewebauthn/server's generateAssertionOptions(...)
+ */
+export default async function startAuthentication(
+  requestOptionsJSON: PublicKeyCredentialRequestOptionsJSON,
+): Promise<AuthenticationCredentialJSON> {
+  if (!browserSupportsWebauthn()) {
+    throw new Error('WebAuthn is not supported in this browser');
+  }
+
+  // We need to avoid passing empty array to avoid blocking retrieval
+  // of public key
+  let allowCredentials;
+  if (requestOptionsJSON.allowCredentials?.length !== 0) {
+    allowCredentials = requestOptionsJSON.allowCredentials?.map(toPublicKeyCredentialDescriptor);
+  }
+
+  // We need to convert some values to Uint8Arrays before passing the credentials to the navigator
+  const publicKey: PublicKeyCredentialRequestOptions = {
+    ...requestOptionsJSON,
+    challenge: base64URLStringToBuffer(requestOptionsJSON.challenge),
+    allowCredentials,
+  };
+
+  // Wait for the user to complete assertion
+  const credential = (await navigator.credentials.get({ publicKey })) as AuthenticationCredential;
+
+  if (!credential) {
+    throw new Error('Authentication was not completed');
+  }
+
+  const { id, rawId, response, type } = credential;
+
+  let userHandle = undefined;
+  if (response.userHandle) {
+    userHandle = bufferToUTF8String(response.userHandle);
+  }
+
+  // Convert values to base64 to make it easier to send back to the server
+  return {
+    id,
+    rawId: bufferToBase64URLString(rawId),
+    response: {
+      authenticatorData: bufferToBase64URLString(response.authenticatorData),
+      clientDataJSON: bufferToBase64URLString(response.clientDataJSON),
+      signature: bufferToBase64URLString(response.signature),
+      userHandle,
+    },
+    type,
+    clientExtensionResults: credential.getClientExtensionResults(),
+  };
+}