# Request signing

You need to specify your **secret key**, apply `SHA256` encryption to your payload and convert the result to `HEX` format

## Nonce usage

You should pass `nonce` parameter in the payload of every request to this API. `nonce` can be a number or a string, each request must be accompanied by a unique value. Otherwise the request will fail.

We will use Unix TimeStamp as the `nonce` value for sending requests in this document.

## Example of creating request signature `NodeJS`

Let's say we want to get price rate of `ETH`/`USDT` (method `/price-rate`)

**1. Build request payload**

```javascript
const payload = { from: 'ETH', to: 'USDT' };
```

**2. Add** **`nonce`** **parameter to the payload in order to avoid request duplication.**

By using unix timestamp as `nonce` parameter we will meet the requirements of using number and its incrementing for every new request.

```javascript
payload.nonce = Date.now(); // 1643881172430
```

**3. Create string from payload and used it in a process of creating signature.**

```javascript
const stringPayload = JSON.stringify(payload); // {"from":"ETH","to":"USDT","nonce":1643881172430}
```

**4. Create signature:**

Example with `crypto-js` module:

```javascript
const CryptoJS = require("crypto-js"); 
const sign = CryptoJS.HmacSHA256(stringPayload, __PRIVATE_KEY__).toString(CryptoJS.enc.Hex)
```

Example with `crypto` module:

```javascript
const crypto = require('crypto');  
const sign = crypto.createHmac('SHA256', __PRIVATE_KEY__).update(stringPayload).digest('hex');
```

**5. Send request with required headers:**

```javascript
const axios = require('axios'); // lib for HTTP requests
const response = await axios.post(__BASE_URL__ + '/price-rate', stringPayload, 
{ 
    headers: 
        {
            'x-api-public-key': __PUBLIC_KEY__, 
            'x-api-signature': sign 
        } 
});
```

**6. Response:**

```javascript
console.log(response.data); // {"success":true,"response":"2751.51000000"}
```