AC-2653: Fix an admin custom URL functionality

Author: arhiopterecs

app/code/Magento/Security/Model/AdminSessionsManager.php

@@ -305,7 +305,7 @@ protected function createNewSession()
         $user = $this->authSession->getUser();
         if (null === $user) {
            $this->processLogout();
-           throw new LocalizedException(__('User is not found'));
+           throw new LocalizedException(__('User not found'));
         }
 
         $adminSessionInfo = $this->adminSessionInfoFactory

app/code/Magento/Security/i18n/en_US.csv

@@ -29,3 +29,4 @@ None,None
 """%1"" must be later than the current date.","""%1"" must be later than the current date."
 "User Expiration","User Expiration"
 """%1"" is not a valid date.","""%1"" is not a valid date."
+"User not found","User not found"