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

# API Authentication

> How to authenticate yourself to use the Valyx API.

# Authentication

All Valyx API requests require authentication using a signature-based header.\
If the signature is missing or invalid, the API will respond with an **HTTP 401 Unauthorized** error.

## Header Required

| Header Name         | Required | Description                                                        |
| ------------------- | -------- | ------------------------------------------------------------------ |
| `X-Valyx-Signature` | Yes      | The HMAC signature used to verify the authenticity of the request. |

***

## How It Works

The `X-Valyx-Signature` is generated using your **Valyx API Secret**.\
When you send a request:

1. Concatenate specific request components (method, path, timestamp, and body) into a string.
2. Sign the string using **HMAC-SHA256** with your API Secret.
3. Encode the result as a hexadecimal string.
4. Add it to the request headers as `X-Valyx-Signature`.

***

## Example Request

```bash theme={null}
curl -X GET "https://api.valyx.com/billing/usageDriver/filter" \
  -H "Content-Type: application/json" \
  -H "X-Valyx-Signature: 7d6a9b8c3f1a4e..." 
```