LL::NG is able to transfer (trough REST or SOAP) authentication credentials to another LL::NG portal, like a proxy.
The difference with remote authentication is that the client will never be redirect to the main LL::NG portal. This configuration is usable if you want to expose your internal SSO portal to another network (DMZ).
In Manager, go in
General Parameters >
Authentication modules and choose Proxy for authentication and users.
Then, go in