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

# Authentication

> How SendyKit API authentication works

## Supported auth modes

SendyKit supports three auth patterns:

| Mode            | Header                      | When to use                                  |
| --------------- | --------------------------- | -------------------------------------------- |
| API key         | `X-API-Key`                 | Standard integrations, operators, automation |
| JWT             | `Authorization: Bearer ...` | User/session-scoped browser or admin flows   |
| Machine payment | `X-Stripe-Machine-Payment`  | Premium actions for agent workflows          |

## API key

This is the primary auth surface for integrations.

```bash theme={null}
curl -H "X-API-Key: sk_a1b2c3d4..." \
  https://your-server.com/sendykit/api/v2/brands
```

## JWT

Use JWTs for session-style flows.

```bash theme={null}
curl -X POST https://your-server.com/sendykit/api/v2/auth/token \
  -d '{"username": "admin", "password": "..."}'
```

Then:

```bash theme={null}
curl -H "Authorization: Bearer eyJ..." \
  https://your-server.com/sendykit/api/v2/brands
```

## Machine payments

For premium actions, SendyKit can require Stripe-native machine-payment proof.

```bash theme={null}
curl -H "X-API-Key: sk_a1b2c3d4..." \
  -H "X-Stripe-Machine-Payment: <payment-proof-or-intent-ref>" \
  https://your-server.com/sendykit/api/v2/ai/subject-lines
```

<Note>
  Current implementation target is Stripe-native machine payments. Raw/direct x402 should be treated as historical exploration, not the live customer path.
</Note>

## Related source of truth

* `docs/AUTH-BILLING-MATRIX.md`
* `docs/openapi/sendykit-v2.yaml`
* `internal/http/middleware_billing.go`