Magento 2.2.2 Plugin how to add custom field in request api

Question

I've create a plugin to listen to api POST /V1/order/:orderId/refund

and I would like to receive custom field. I've added a field for testing like: name:['test']

Body E.G:

{
    "items": [
        {
            "extension_attributes": {},
            "order_item_id": 7,
            "qty": 1
        }
    ],
    "isOnline": false,
    "notify": true,
    "appendComment": true,
    "name": [
      { 
          "test": "ok" 
      }
    ], //THIS IS MY CUSTOM FIELD
    "comment": {
        "extension_attributes": {},
        "comment": "refund has been created",
        "is_visible_on_front": 0
    },
    "arguments": {
        "shipping_amount": 0,
        "adjustment_positive": 0,
        "adjustment_negative": 0,
        "extension_attributes": {
            "return_to_stock_items": []
        }
    }
}

beforeExecute Method:

...
    /**
     * Create refund for invoice
     *
     * @param int $invoiceId
     * @param \Magento\Sales\Api\Data\CreditmemoItemCreationInterface[] $items
     * @param bool|null $isOnline
     * @param bool|null $notify
     * @param bool|null $appendComment
     * @param \Magento\Sales\Api\Data\CreditmemoCommentCreationInterface|null $comment
     * @param \Magento\Sales\Api\Data\CreditmemoCreationArgumentsInterface|null $arguments
     * @param mixed $name
     * @return int
     * @since 100.1.3
     */

    public function beforeExecute (
        \Magento\Sales\Model\RefundOrder $subject,
        $orderId,
        array $items = [],
        $notify = false,
        $appendComment = false,
        \Magento\Sales\Api\Data\CreditmemoCommentCreationInterface $comment = null,
        \Magento\Sales\Api\Data\CreditmemoCreationArgumentsInterface $arguments = null,
        array $name = []
    ) {
        print_r($name);die;
      }
...

My custom field name is an array similar to items: but I am receiving an empty array from Response:

Anyone any help Appreciated!

Answer 1

It does not fully answer my question but it helps, we can add custom_attribute to any extension_attributes I've used the arguments by doing the following :

create vendor/module/etc/extension_attributes.xml:

... <extension_attributes for="Magento\Sales\Api\Data\CreditmemoCreationArgumentsInterface">
        <attribute code="name" type="string" />
    </extension_attributes> ...

Block doc : * @param \Magento\Sales\Api\Data\CreditmemoCreationArgumentsInterface|null $name

beforeExecute method:

...\Magento\Sales\Api\Data\CreditmemoCreationArgumentsInterface $name = null,...

then:

print_r($arguments->getExtensionAttributes()->getName());

Wallahhhh!