Manual of sending a request

There is an example of how to generate the X-Api-Signature parameter and send a request with Node.js:

Find a module that supports generating an RSA signature using the SHA256 hashing algorithm.

note

For Node.js, it is a crypto module. If you use another programming language in your project, you should find a similar module supported by your language.

Find a module that allows sending HTTP requests.

note

For Node.js, it is a node-fetch module.

Install the needed modules in any convenient way. For example, with npm:

npm install crypto
npm install node-fetch

Import the modules to your code:

const crypto = require('crypto');
const fetch = require('node-fetch');      

Define the variables for your private and public keys:

const API_PUBLIC_KEY = '<Your public API key>';
const API_PRIVATE_KEY = '<Your private API key>';

Create a private key object with the following type, format and encoding:

const privateKeyObject = crypto.createPrivateKey({
  key: API_PRIVATE_KEY,
  type: 'pkcs1',
  format: 'pem',
  encoding: 'base64',
});

Define the variables for the URL and body message of the API method you want to request. For example:

const path = 'https://fiat-api.changelly.com/v1/validate-address';
const message = {
  "currency": "XRP",
  "walletAddress": "rwpMvfxoodXggJ1g4qv6MWAPQqWDwQyHUW",
  "walletExtraId": "1234hg"
};   

To provide path or query request parameters, specify them in the path variable, for example:

const path = 'https://fiat-api.changelly.com/v1/currencies?type=crypto';

Important! This message example is applied to the POST request. If you want to send GET request, you should make the message empty:

const message = {};

If you delete the message variable, you will get an error.

Concatenate the path and the message object into one string:

const payload = path + JSON.stringify(message);

Create a signature that will be used as X-Api-Signature header:

const signature = crypto.sign('sha256', Buffer.from(payload), privateKeyObject).toString('base64');

crypto.sign takes as input 3 parameters:

hashing algorithm – sha256.
request data – Buffer.from(payload).
private key object in the desired format – privateKeyObject.

crypto.sign returns signature in a buffer. You need to convert it to base64 format.

Create an options object which contains info for API request – HTTP method, headers and body:

const options = {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Api-Key': API_PUBLIC_KEY,
    'X-Api-Signature': signature,
  },
  body: JSON.stringify(message),
};

Send a request:

fetch(path, options).then(response => {
  if (response.ok) {
    return response.json();
  }
  throw new Error(`Request error: ${response.status} ${response.statusText}`);
}).then((response) => {
  console.log('Successful response: ', response);
}).catch(error => {
  console.error(error);
});