---
title: "Begin passkey sign-in — return WebAuthn assertion options"
method: POST
path: "/auth/passkey/challenge"
tags: ["Auth"]
---

# Begin passkey sign-in — return WebAuthn assertion options

`POST /auth/passkey/challenge`

## Request

- Base URL: `https://api.mnemom.ai/v1`
- URL: `https://api.mnemom.ai/v1/auth/passkey/challenge`
- Auth: none required

Unauthenticated. Returns `PublicKeyCredentialRequestOptions` with an empty `allowCredentials` list (discoverable-credentials flow). The browser surfaces any matching passkey for this RP without needing the user to enter an email. Rate-limited.

## Response `200`

WebAuthn assertion options.

- PublicKeyCredentialRequestOptionsJSON: WebAuthn authentication options.
  - `rpId` string
  - `challenge` string
  - `userVerification` string
  - `allowCredentials` unknown[]
    - unknown
  - `timeout` integer

## Other responses

- `403`: Forbidden
- `429`: Rate-limit exceeded. The global per-IP limiter (100 requests/minute, applied to every `/v1/*` route) rejected this request. Back off until the window resets — `Retry-After` carries the cooldown in seconds and `X-RateLimit-Reset` the absolute reset time.
- `500`: Server error — request was well-formed but the server failed to fulfill it. Typically a downstream dependency (DB / RPC / external API) returned an unexpected error.
- `503`: An upstream dependency is currently unavailable. The request was not processed; retry after the cooldown window.

---

[API](https://skmtc.dev/mnemom/apis/mnemom-api.md) · [All operations](https://skmtc.dev/mnemom/apis/mnemom-api/llms.txt) · [OpenAPI document](https://skmtc.dev/mnemom/apis/mnemom-api/revisions/274b7a6ea182?raw)