Controller/Adminhtml/FastlyCdn/BasicAuthentication/Item/Create.php
public function execute()
    {
        $result = $this->resultJson->create();

        try {
            $activeVersion = $this->getRequest()->getParam('active_version');

            $dictionary = $this->api->getAuthDictionary($activeVersion);

            if ((is_array($dictionary) && empty($dictionary)) || !isset($dictionary->id)) {
                return $result->setData([
                    'status'    => 'empty',
                    'msg'       => 'Authentication dictionary does not exist.'
                ]);
            }

            $user = $this->getRequest()->getParam('auth_user');
            $pass = $this->getRequest()->getParam('auth_pass');
            $key = base64_encode($user . ':' . $pass);
            $this->api->upsertDictionaryItem($dictionary->id, $key, true);

            return $result->setData(['status' => true]);
        } catch (\Exception $e) {
            return $result->setData([
                'status'    => false,
                'msg'       => $e->getMessage()
            ]);
        }
    }
public function execute()
    {
        $result = $this->resultJson->create();

        try {
            $activeVersion = $this->getRequest()->getParam('active_version');

            $dictionary = $this->api->getAuthDictionary($activeVersion);

            if ((is_array($dictionary) && empty($dictionary)) || !isset($dictionary->id)) {
                return $result->setData([
                    'status'    => 'empty',
                    'msg'       => 'Authentication dictionary does not exist.'
                ]);
            }

            $user = $this->getRequest()->getParam('auth_user');
            $pass = $this->getRequest()->getParam('auth_pass');
            $key = base64_encode($user . ':' . $pass);
            $this->api->upsertDictionaryItem($dictionary->id, $key, true);

            return $result->setData(['status' => true]);
        } catch (\Exception $e) {
            return $result->setData([
                'status'    => false,
                'msg'       => $e->getMessage()
            ]);
        }
    }
Create auth item

@return \Magento\Framework\App\ResponseInterface|\Magento\Framework\Controller\Result\Json|\Magento\Framework\Controller\ResultInterface