SAML 2.0 is a web standard used for Single Sign-On (SSO) in enterprise environments. It issues XML tokens for authentication, which allows for secure and seamless access across different applications and services within an organization. While OAuth is also used in authentication contexts, it does not primarily focus on issuing XML tokens for SSO. RADIUS and LDAP are used for different aspects of network access and directory services, respectively, but are not primarily focused on issuing XML tokens for SSO.