This API allows people to use the Playstation Network SignIn for their own sites. If a developer's site URL is allowed by Sony, they can set their site as the returnURL by GET. This allows them to bypass Sony's official External PSN Sign In page. The site forwards to a developer's site on a successful sign in with a sessionId by GET. There is no official public API to convert the sessionId into a user specific value (like the PSN-ID). The API converts a valid sessionID into a proper PSN-ID.