redirect to backend if request uri isn't valid

Author: engcom-Charlie

app/code/Magento/Backend/Controller/Adminhtml/Auth/Login.php

@@ -48,6 +48,11 @@ public function execute()
             return $this->getRedirect($this->_backendUrl->getStartupPageUrl());
         }
 
+        $requestUrl = $this->getRequest()->getUri();
+        if (!$requestUrl->isValid()) {
+            return $this->getRedirect($this->getUrl('*'));
+        }
+
         return $this->resultPageFactory->create();
     }
 

app/code/Magento/User/Controller/Adminhtml/User/Save.php

@@ -105,7 +105,7 @@ public function execute()
             $this->getSecurityCookie()->setLogoutReasonCookie(
                 \Magento\Security\Model\AdminSessionsManager::LOGOUT_REASON_USER_LOCKED
             );
-            $this->_redirect('adminhtml/*/');
+            $this->_redirect('*');
         } catch (NotificationExceptionInterface $exception) {
             $this->messageManager->addErrorMessage($exception->getMessage());
         } catch (\Magento\Framework\Exception\AuthenticationException $e) {