<?php
$endpoint_url="your_url_here";
$string_json = "your_json_string";
$username="username";
$password ="password";

$client = new Client();
$options= array(
  'auth' => [
    $username,
    $password
  ],
  'headers'  => ['content-type' => 'application/json', 'Accept' => 'application/json'],
  'body' => $string_json,
  "debug" => true
);
try {
  $res = $client->post($endpoint_url, $options);
} catch (ClientException $e) {
  echo $e->getRequest() . "\n";
  if ($e->hasResponse()) {
    echo $e->getResponse() . "\n";
  }
}
echo "OO<h1>".$res->getStatusCode()."</h1>OO";