Am I right, that LdapAuthentication.php at present does not offer a single_sign-on access but "only" the security of authentication, so that only authorized people have access to the company's wiki?

Well, it depends on what you mean. Single sign on is kind of a generic term.

The LDAP Authentication plugin does support CAC/Smartcard authentication, and most auto-auth plugins can be (slightly) modified to work with the LDAP plugin.

If you mean kerberos or ntlm, neither one currently work with the plugin.