/**
     *
     * {@inheritDoc}
     * @see IotaEShoppingApiStoreManagementInterface::getOptionsOfConfigurationProduct()
     */
    public function getOptionsOfConfigurationProduct($productId) {
        $product = $this->productFactory->create()->load($productId);
        $extensionAttributes = $product->getExtensionAttributes();
        $configurableProductOptions = $extensionAttributes->getConfigurableProductOptions();
        $options = $product->getOptions();
        $childProduct = $product->getTypeInstance()->getUsedProducts($product);
        $productAttributeOptions = array();
        foreach ($configurableProductOptions as $option) {
            $optionValues = array();
            foreach ($option->getValues() as $optionValue) {
                $optionValues[] = $optionValue->getData();
            }
            $children = array();
            foreach ($childProduct as $child) {
                $children[] = $child->getData();
            }
            $productAttributeOptionArray = $option->getData();
            $productAttributeOptionArray['values'] = $optionValues;
            $productAttributeOptionArray['child'] = $children ;
            $productAttributeOptions[] = $productAttributeOptionArray;
        }

        $productOptions = array();
        foreach ($options as $option) {
            $optionValue = array();
            foreach ($option->getValues() as $value) {
                $optionValue[] = $value->getData();
            }
            $productOptionArray = $option->getData();
            $productOptionArray['values'] = $optionValue;
            $productOptions[] = $productOptionArray;
        }

        $result = array(
            'extension_attributes' => array('configurable_product_options' => $productAttributeOptions),
            'options' => $productOptions
        );
        return [$result];
    }

[
    {
        "extension_attributes": {
            "configurable_product_options": [
                {
                    "product_super_attribute_id": "160",
                    "product_id": "962",
                    "attribute_id": "141",
                    "position": "0",
                    "product_attribute": {},
                    "label": "Size",
                    "use_default": "0",
                    "options": [
                        {
                            "value_index": "5",
                            "label": "S",
                            "product_super_attribute_id": "160",
                            "default_label": "S",
                            "store_label": "S",
                            "use_default_value": true
                        },
                        {
                            "value_index": "6",
                            "label": "M",
                            "product_super_attribute_id": "160",
                            "default_label": "M",
                            "store_label": "M",
                            "use_default_value": true
                        }
                    ],
                    "values": [
                        {
                            "value_index": "5"
                        },
                        {
                            "value_index": "6"
                        }
                    ],
                    "child": [
                        {
                            "entity_id": "960",
                            "attribute_set_id": "4",
                            "type_id": "simple",
                            "sku": "Food With Option 1-S",
                            "has_options": "0",
                            "required_options": "0",
                            "created_at": "2018-06-05 09:40:24",
                            "updated_at": "2018-06-05 09:40:24",
                            "parent_id": "962",
                            "catalog_rule_price": null,
                            "name": "Food With Option 1-S",
                            "url_key": "food-with-option-1-s",
                            "status": "1",
                            "tax_class_id": "0",
                            "koi_size": "5",
                            "price": "1.0000",
                            "weight": "1.0000",
                            "media_gallery": {
                                "images": [],
                                "values": []
                            },
                            "tier_price": [],
                            "tier_price_changed": 0
                        },
                        {
                            "entity_id": "961",
                            "attribute_set_id": "4",
                            "type_id": "simple",
                            "sku": "Food With Option 1-M",
                            "has_options": "0",
                            "required_options": "0",
                            "created_at": "2018-06-05 09:40:25",
                            "updated_at": "2018-06-05 09:40:25",
                            "parent_id": "962",
                            "catalog_rule_price": null,
                            "name": "Food With Option 1-M",
                            "url_key": "food-with-option-1-m",
                            "status": "1",
                            "tax_class_id": "0",
                            "koi_size": "6",
                            "price": "1.0000",
                            "weight": "1.0000",
                            "media_gallery": {
                                "images": [],
                                "values": []
                            },
                            "tier_price": [],
                            "tier_price_changed": 0
                        }
                    ]
                }
            ]
        },
        "options": []
    }
]