I am trying to connect our Active directory server to brand new RHEL 6.5 server. I want to authenticate users using AD credentials, but I want to restrict that only certain users can login, I don't want to allow anybody from AD to connect to it. I would like to use something like this:

CN=linuxtest,OU=SecurityGroups,DC=mydomain,DC=local

but I am not sure how would I setup OU and CN. I use sssd for authentication and my id_provider = ad. I wanted to use id_provider = ldap, but that did not work at all and RHEL customer service told me to setup this way. But I want to have a little bit more control who can do what. I know I can use this to restrict simple_allow_users = user1, user2, but I have 400+ users, I really don't want to go and type them all. Question is how would I setup OU or CN for my search?