Steps to reproduce:

1. Login
2. Wait for auto log out (to speed up can change users.autologout field to 10s)
3. Press "Sign out"

Result:
Warning in error log

PHP Warning:  Undefined array key "secret" in /home/zabbix/git.zabbix.com/tags/6.4.0/ui/include/classes/helpers/CCsrfTokenHelper.php on line 37

Expected:
No errors.