Currently can do this with authorizer_allow_login, authorizer_custom_role, and authorizer_automatically_approve_login hooks, but a UI for defining the mappings would be nice.
Implement an extra tab on the Authorizer options page that has a list of rules that you've defined. Would need to cache possible attributes from prior logins to show suggestions to users. (Probably should only cache attributes, not values, because of potential sensitive data).