Magento 2 REST API – How to Post a Product Attribute

I'm new in Magento 2, I want to add an attribute using REST api. Is it possible? I use the follow code for products:

<?php 
    ini_set('display_errors', 1);
    ini_set('display_startup_errors', 1);
    error_reporting(E_ALL);


$url = "http://mywebsite/";
$token_url = $url."rest/V1/integration/admin/token";
$product_url = $url. "rest/V1/products";
$username = "myUserName";
$password = "myPassword";



$ch = curl_init();
$data = array("username" => $username, "password" => $password);
$data_string = json_encode($data);
$ch = curl_init($token_url);
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))
    );
$token = curl_exec($ch);
$adminToken=  json_decode($token);


$sampleProductData = array(
        'sku'               => 'config_product-small-red',
        'name'              => 'Simple Product ' . uniqid(),
        'visibility'        => 4, /*'catalog',*/
        'type_id'           => 'simple',
        'price'             => 99.95,
        'status'            => 1,
        'attribute_set_id'  => 4,
        'weight'            => 1,
        'custom_attributes' => array(
            array( 'attribute_code' => 'category_ids', 'value' => ["42","41","32"] ),
            array( 'attribute_code' => 'description', 'value' => 'Simple Description' ),
            array( 'attribute_code' => 'short_description', 'value' => 'Simple Short Description' ),
          array( 'attribute_code' => 'size', 'value' => '5' ), //5=small
          array( 'attribute_code' => 'color', 'value' => '8' ), //8-red
            ),
    'extension_attributes' => array(
        "stock_item"=>array(
            "qty"=>10,
            "is_in_stock"=>true,
        ),

    )
    );
$productData = json_encode(array('product' => $sampleProductData));
$setHaders = array('Content-Type:application/json','Authorization:Bearer '.$adminToken);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $product_url);
curl_setopt($ch, CURLOPT_POSTFIELDS, $productData);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_HTTPHEADER, $setHaders);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);
var_dump($response);

?>

How can I do the same for product attributes?