The IdP Proxy provides AAI services for both service providers and users.
For the user the feature is transparent: as soon as their IdP is integrated with the proxy, they are redirected by the service to their own IdP. Once integrated the IdP with the proxy, all the services using the IdP proxy will be available.
The service providers will get all the AuthN/AuthZ information needed from the IdP Proxy (in form of attributes), without the need to deal with individual IdPs.
Other components that can be attached to the IdP Proxy are credential translation services and attribute authorities.