This document analyzes single sign-on (SSO) authentication for web applications, specifically using Google as a service provider. It discusses problems with traditional username and password authentication across multiple systems and how SSO solves this by allowing a user to log in once to access all authorized resources. The document then provides details on how SSO authentication works for Google applications using Security Assertion Markup Language (SAML). It describes the steps a user takes to log into a Google application through a partner-operated SSO service, including SAML requests and responses being passed between the partner SSO, user's browser, and Google.