$data_string = '

    "method": "countriesList",

    "username": "api_user",

    "password": "api_password"

';

$ch = curl_init('https://...');

curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");

curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);

curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

curl_setopt($ch, CURLOPT_HTTPHEADER, array(

'Content-Type: application/json',

'Content-Length: ' . strlen($data_string))

);

$result = curl_exec($ch);

echo $result;