Hi,
Have you test your kerberos authentication is working or not? you need to proof this first between the LMS server and Active Directory server by using the command line (if LMS is in linux server).
Then after that, you can start to configure the apache in LMS setting page. The default authentication also should be set to Apache and same with the order if login method.
Dont forget to tick in apache configuration in LMS that 'enable the user creation based on LDAP'. in LDAP setting page, tick the synch when do 'login'.
In addition, if you are using IE, you need to enable the Integrated Windows Authentication (IWA) at internet option setting.
Then if all okay, the SSO should working.