---
title: "Request a challenge nonce for agent authentication"
method: POST
path: "/agent/challenge"
---

# Request a challenge nonce for agent authentication

`POST /agent/challenge`

Returns a one-time nonce that must be signed by the agent's sr25519 key. Nonce expires in 60 seconds.

## Request body

- AgentChallengeRequest
  - `address` string, required — Vara account address (SS58 or hex)

## Response `200`

Challenge created

## Other responses

- `400` — Invalid address
- `429` — Rate limited

## Changes

- **2026-07-17** `3753ad0069f9` — 1 info
  - endpoint added
- **2025-01-20** `12a1d58831ef` — 1 breaking
  - api path removed without deprecation

[Change history](https://skmtc.dev/gear-tech/apis/api-documentation/changes/agent/challenge/post.md)

---

[API](https://skmtc.dev/gear-tech/apis/api-documentation.md) · [All operations](https://skmtc.dev/gear-tech/apis/api-documentation/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/gear-tech/api-documentation/revisions/3753ad0069f9/schema)