An increasing number of federated social logons, like , do require the user to enter consent choices upon first registration with a new resource, and so are not always single sign-on in the strictest sense.
Authentication scheme Single sign-on SSO is an authentication scheme that allows a user to with a single ID and password to any of several related, yet independent, software systems.
There are also some specific systems that commonly come up when we are discussing Single Sign-on: Active Directory, Active Directory Federation Services ADFS and Lightweight Directory Access Protocol LDAP.
