A service to guide a user to his or her Identity Provider.
The goal of a "Where Are You From" (WAYF) service is to guide a user to his or her Identity Provider. Some documentation also calls this the "Identity Provider Discovery" service.
Basically, all the WAYF has to accomplish, is to present the user a list of Identity Providers and redirect the user's web browser to the selected Identity Provider (IdP) or back to the Service Provider (the web application that the user is trying to access). Some WAYFs have additional features which enhance the user's ease-of use. This includes several methods of remembering or guessing the user's Identity Provider selection. Usually by storing a persistent cookie which indicates the user's previous choice of Identity Provider.