[Apiman-user] applications without plans?

I'm wanting to do something that may not be possible :-) I have a service that I want to offer to multiple organisations. I want the users of each organisation to authenticate according to the needs or that organisation (e.g. against their own LDAP server). I do not want to have to handle API keys as I have lots of organisations and lots of services and lots of versions of those services, so think managing those keys will fast become a nightmare. I am happy to use the service as a public service, as long as the user is authenticated and authorized. e.g. I think what I want to do is create an application in each organisation with a policy that does the authentication, and use a public service that does the authorization based on expected role granted to the user. But the only way I can see to do this is to use plans, which involve the need for API keys. Any ways to do this? Tim