> ## Documentation Index
> Fetch the complete documentation index at: https://agentcash.dev/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Authenticated requests

> Use SIWX (Sign-In With X) for endpoints that require wallet identity.

Some endpoints require wallet-based authentication, either on its own or alongside payment. This uses the **SIWX** (Sign-In With X) protocol, where your wallet signs a challenge to prove its identity.

## How SIWX works

<Steps>
  <Step title="Request triggers a 402 with SIWX challenge">
    The endpoint responds with `402 Payment Required` and includes a SIWX challenge, either on its own or alongside a payment requirement.
  </Step>

  <Step title="AgentCash signs the challenge">
    Your wallet signs the server's challenge to prove ownership of the address.
  </Step>

  <Step title="Request retries with auth headers">
    AgentCash retries the original request with the signed proof in the headers.
  </Step>
</Steps>

## Making authenticated requests

Ask your agent to use `fetch`:

> Use AgentCash fetch to call [https://example.com/api/protected-endpoint](https://example.com/api/protected-endpoint).

Or via CLI:

```bash theme={null}
npx agentcash fetch https://example.com/api/protected-endpoint
```

AgentCash handles the full SIWX handshake automatically and only falls back to payment if the route still returns `402`.

## When to use authenticated vs paid requests

| Scenario                               | Tool / command                          |
| -------------------------------------- | --------------------------------------- |
| Endpoint requires USDC payment         | `fetch`                                 |
| Endpoint requires wallet identity only | `fetch`                                 |
| Not sure which auth the endpoint uses  | `check_endpoint_schema` / `check` first |

<Tip>
  Use `check_endpoint_schema` (MCP) or `npx agentcash check` (CLI) to inspect an endpoint before calling it. The response tells you whether it requires payment, SIWX auth, or both, but `fetch` handles every case.
</Tip>