The classic single sign-on (SSO) use case is the single sign-on between a single client and multiple back end services. A user accesses multiple back end servers through a single UI client. The user provides credentials to the UI client only once, which validates them against the SSO server. If the validation is successful, the SSO server issues a SAML token which then can be used by the UI client to access other back end servers. The following figure illustrates this use case.