Just use kerberos. You don't need LDAP to use Kerberos (although you probably should be using LDAP too). Kerberos without LDAP is trivial to set-up and administer, and it's very non-invasive, so you don't need to do any significant changes to your organization.
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Extraordinarily useful on an internal corporate network, especially when you're scp'ing remote->remote and so on.
Just use kerberos. You don't need LDAP to use Kerberos (although you probably should be using LDAP too). Kerberos without LDAP is trivial to set-up and administer, and it's very non-invasive, so you don't need to do any significant changes to your organization.