---
title: "Authenticate Start"
method: POST
path: "/v1/passkeys/authenticate/start"
tags: ["passkeys"]
---

# Authenticate Start

`POST /v1/passkeys/authenticate/start`

## Request

- Base URL: `https://www.tandem-cc.com` (the document declares no server; this is the origin it was published from)
- URL: `https://www.tandem-cc.com/v1/passkeys/authenticate/start`
- Auth: none declared

Begin passkey login.

If the client includes a `handle` hint, we return the credential IDs
registered for that handle so the browser can prompt for the right
one (username-first flow). If not (usernameless / discoverable
credentials flow), we return only the challenge — the authenticator
resolves which credential to use on-device.

## Request body

- object

## Response `200`

Successful Response

- object

## Other responses

- `422`: Validation Error

---

[API](https://skmtc.dev/tandem-cc/apis/tandem-api.md) · [All operations](https://skmtc.dev/tandem-cc/apis/tandem-api/llms.txt) · [OpenAPI document](https://skmtc.dev/tandem-cc/apis/tandem-api/revisions/3b804877b47c?raw)