ACP2E-2070: Wrong X-Magento-Vary after logging-in to the customer account

Author: npuchko

app/code/Magento/Customer/Model/App/Action/ContextPlugin.php

@@ -48,7 +48,7 @@ public function beforeExecute(ActionInterface $subject)
     {
         $this->httpContext->setValue(
             Context::CONTEXT_GROUP,
-            $this->customerSession->getCustomerGroupId(),
+            (string)$this->customerSession->getCustomerGroupId(),
             GroupManagement::NOT_LOGGED_IN_ID
         );
         $this->httpContext->setValue(

app/code/Magento/Customer/Model/Session.php

@@ -211,7 +211,7 @@ public function setCustomerData(CustomerData $customer)
         } else {
             $this->_httpContext->setValue(
                 Context::CONTEXT_GROUP,
-                $customer->getGroupId(),
+                (string)$customer->getGroupId(),
                 \Magento\Customer\Model\Group::NOT_LOGGED_IN_ID
             );
             $this->setCustomerId($customer->getId());
@@ -271,7 +271,7 @@ public function setCustomer(Customer $customerModel)
         $this->_customerModel = $customerModel;
         $this->_httpContext->setValue(
             Context::CONTEXT_GROUP,
-            $customerModel->getGroupId(),
+            (string)$customerModel->getGroupId(),
             \Magento\Customer\Model\Group::NOT_LOGGED_IN_ID
         );
         $this->setCustomerId($customerModel->getId());