Single Sign On is a technology for the user authentication that allows access to multiple applications with one set of user credentials. Single sign on technology promises to address password problems, improve productivity and reduce cost by giving users access to all applications after signing into the network just once.
When software systems have trust with a common identity provider (IdP), they can delegate the responsibility of authenticating the user (with their username and password) to the IdP, but they also have the power to decide what type of access at the application level to authorize the user for.