On a RHEL6 system with a working Kerberos implementation, I can log in using my AD username and password, however the login prompt pops up multiple times per for each page. Also, for every refresh/reload a login is required.

<Directory "/var/www/zabbix">
Options FollowSymLinks
SSLRequireSSL
AllowOverride All
Order allow,deny
Allow from all
AuthType Kerberos
AuthName "Kerberos Login"
require valid-user
KrbVerifyKDC off
#KrbMethodK5Passwd On
KrbMethodNegotiate on
#KrbAuthoritative on
#KrbAuthRealms DOMAIN.TLD
#Krb5Keytab /etc/httpd/conf/apache.keytab
#KrbSaveCredentials on

php_value max_execution_time 300
php_value memory_limit 128M
php_value post_max_size 16M
php_value upload_max_filesize 2M
php_value max_input_time 300
php_value date.timezone America/New_York
</Directory>