ENGCOM-6127: #15959 Extension attributes of quote on checkout page #24771

 - Merge Pull Request #24771 from skylineop/magento2:fix-15959
 - Merged commits:
   1. 2826f74
   2. e818039
   3. 0c7844e

Author: magento-engcom-team

app/code/Magento/Checkout/Model/DefaultConfigProvider.php

@@ -397,6 +397,9 @@ private function getQuoteData()
         if ($this->checkoutSession->getQuote()->getId()) {
             $quote = $this->quoteRepository->get($this->checkoutSession->getQuote()->getId());
             $quoteData = $quote->toArray();
+            if (null !== $quote->getExtensionAttributes()) {
+                $quoteData['extension_attributes'] = $quote->getExtensionAttributes()->__toArray();
+            }
             $quoteData['is_virtual'] = $quote->getIsVirtual();
 
             if (!$quote->getCustomer()->getId()) {