So I might be misinterpreting your question. For your organization, by chance are you already using Active Directory to authenticate? Is it the case that you wanted to add non-company users only for Local Authentication? The reason I ask is at this point in time you really can't have mixed authentication methods. It really would have to be one or the other. If I have misinterpreted your question, Local Authentication requires setting up the user accounts with a Username/Password which you could integrate with SAML.