When using zabbix server frontend in a Single Sign On (SSO) environment one cannot do logout and login as another user (example: as an admin user).

Steps to reproduce:

1. Have apache (example with apache mod_auth_gssapi kerberos enabled for "location" /index_http.php) and the frontend http authentication configured with kerberos SSO with Active Directory (AD)
2. Open zabbix frontend, SSO will log you automatically with your logged in AD user
3. Now try to click the logout button

Result:
Reloads the page (probably logs out and SSO log in again) and you are still logged in.

Expected:
Logout (for instance set a cookie for zabbix server not do the auto SSO login for x seconds). And them allow to login as another user (ex: admin user login).

Further information:

As far as i can tell, logout process in done in js here (https://github.com/zabbix/zabbix/blob/master/frontends/php/js/init.js#L44-L52) and them here in php (https://github.com/zabbix/zabbix/blob/master/frontends/php/index.php#L44-L47).

Redirecting to index.php, which in turn, in zabbix HTTP authetication mode redirects to index_http.php (here https://github.com/zabbix/zabbix/blob/master/frontends/php/index.php#L62-L67), so will SSO login again with current logged in user.