---
title: "Start a SIWE (EIP-4361) wallet login"
method: POST
path: "/v2/auth/siwe/challenge"
tags: ["Orders"]
---

# Start a SIWE (EIP-4361) wallet login

`POST /v2/auth/siwe/challenge`

## Request

- Base URL: `https://execution.kairos.trade`
- URL: `https://execution.kairos.trade/v2/auth/siwe/challenge`
- Auth: none required

Returns the exact EIP-4361 message for `address` to sign (Polygon, chain id 137) and a single-use nonce valid for 5 minutes. **Unauthenticated.** The wallet must already be linked to a Kairos account in the web app ("Link signing wallet"); linking needs a browser session plus step-up and has no API route.

## Request body

- object
  - `address` string, required: The linked EOA that will sign.

## Response `200`

Message to sign with `personal_sign`.

- object
  - `nonce` string, required
  - `message` string, required
  - `expires_at_us` integer, required: Challenge expiry, unix microseconds.

## Other responses

- `400`: `invalid address`.
- `503`: `SIWE login is not configured on this deployment`.

---

[API](https://skmtc.dev/kairos/apis/kairos-order-execution-api.md) - [All operations](https://skmtc.dev/kairos/apis/kairos-order-execution-api/llms.txt) - [OpenAPI document](https://skmtc.dev/kairos/apis/kairos-order-execution-api/revisions/9ba7d463d505?raw)