Official SDK

/**
 * generate sign
 **/
private String toSign(String timestamp, String method, String requestPath,
                             String queryString, String body, String secretKey) throws Exception {
    // sign
    String preHash = preHash(timestamp, method, requestPath, queryString, body);
    byte[] secretKeyBytes = secretKey.getBytes("UTF-8");
    SecretKeySpec secretKeySpec = new SecretKeySpec(secretKeyBytes, "HmacSHA256");
    Mac mac = (Mac) MAC.clone();
    mac.init(secretKeySpec);
    return Hex.encodeHexString(mac.doFinal(preHash.getBytes("UTF-8")));
}

/**
 * sign
 **/
private String preHash(String timestamp, String method, String requestPath, String queryString, String body) {
                                 
    StringBuilder preHash = new StringBuilder();
    preHash.append(timestamp);
    preHash.append(method.toUpperCase());
    preHash.append(requestPath);
    if (org.apache.commons.lang3.StringUtils.isNotEmpty(queryString)) {
        preHash.append("?").append(queryString);
    }
    if (org.apache.commons.lang3.StringUtils.isNotEmpty(body)) {
        preHash.append(body);
    }
    return preHash.toString();
}

/**
 * queryString
 **/
private String queryString(ServerHttpRequest request) {
    String url = request.getURI().toString();
    String queryString = "";
    if (url.contains("?")) {
        queryString = url.substring(url.lastIndexOf("?") + 1);
    }
    return queryString;
}

OkHttpClient client = new OkHttpClient().newBuilder()
  .build();
MediaType mediaType = MediaType.parse("application/json");
RequestBody body = RequestBody.create(mediaType, "{\"symbol\":\"BTCUSDT\",\"volume\":1,\"side\":\"BUY\",\"type\":\"LIMIT\",\"price\":10000,\"newClientOrderId\":\"\",\"recvWindow\":5000}");
Request request = new Request.Builder()
  .url("https://openapi.idax.exchange")
  .method("POST", body)
  .addHeader("X-CH-APIKEY", "Your API key")
  .addHeader("X-CH-TS", "1596543296058")
  .addHeader("Content-Type", "application/json")
  .addHeader("X-CH-SIGN", "encrypt sign")
  .build();
Response response = client.newCall(request).execute();

package main

import (
  "fmt"
  "strings"
  "net/http"
  "io/ioutil"
)

func main() {

  url := "https://openapi.idax.exchange"
  method := "POST"

  payload := strings.NewReader("{\"symbol\":\"BTCUSDT\",\"volume\":1,\"side\":\"BUY\",\"type\":\"LIMIT\",\"price\":10000,\"newClientOrderId\":\"\",\"recvWindow\":5000}")

  client := &http.Client {
  }
  req, err := http.NewRequest(method, url, payload)

  if err != nil {
    fmt.Println(err)
  }
  req.Header.Add("X-CH-APIKEY", "Your API key")
  req.Header.Add("X-CH-TS", "1596543881257")
  req.Header.Add("Content-Type", "application/json")
  req.Header.Add("X-CH-SIGN", "encrypt sign")

  res, err := client.Do(req)
  defer res.Body.Close()
  body, err := ioutil.ReadAll(res.Body)

  fmt.Println(string(body))
}

import requests

url = "https://openapi.idax.exchange"

payload = "{\"symbol\":\"BTCUSDT\",\"volume\":1,\"side\":\"BUY\",\"type\":\"LIMIT\",\"price\":10000,\"newClientOrderId\":\"\",\"recvWindow\":5000}"
headers = {
  'X-CH-APIKEY': 'Your API key',
  'X-CH-TS': '1596543881257',
  'Content-Type': 'application/json',
  'X-CH-SIGN': 'encrypt sign'
}

response = requests.request("POST", url, headers=headers, data = payload)

print(response.text.encode('utf8'))

<?php
require_once 'HTTP/Request2.php';
$request = new HTTP_Request2();
$request->setUrl('https://openapi.idax.exchange');
$request->setMethod(HTTP_Request2::METHOD_POST);
$request->setConfig(array(
  'follow_redirects' => TRUE
));
$request->setHeader(array(
  'X-CH-APIKEY' => 'Your API key',
  'X-CH-TS' => '1596543881257',
  'Content-Type' => 'application/json',
  'X-CH-SIGN' => 'encrypt sign'
));
$request->setBody('{"symbol":"BTCUSDT","volume":1,"side":"BUY","type":"LIMIT","price":10000,"newClientOrderId":"","recvWindow":5000}');
try {
  $response = $request->send();
  if ($response->getStatus() == 200) {
    echo $response->getBody();
  }
  else {
    echo 'Unexpected HTTP status: ' . $response->getStatus() . ' ' .
    $response->getReasonPhrase();
  }
}
catch(HTTP_Request2_Exception $e) {
  echo 'Error: ' . $e->getMessage();
}

var request = require('request');
var options = {
  'method': 'POST',
  'url': 'https://openapi.idax.exchange',
  'headers': {
    'X-CH-APIKEY': 'Your API key',
    'X-CH-TS': '1596543881257',
    'Content-Type': 'application/json',
    'X-CH-SIGN': 'encrypt sign'
  },
  body: JSON.stringify({"symbol":"BTCUSDT","volume":1,"side":"BUY","type":"LIMIT","price":10000,"newClientOrderId":"","recvWindow":5000})

};
request(options, function (error, response) {
  if (error) throw new Error(error);
  console.log(response.body);
});