Single Sign-On (SSO) is a feature that connects multiple applications through one password. It makes life simple, by eliminating the need to remember multiple passwords, and allows you to login once and access many systems.
Federated authentication using Security Assertion Markup Language (SAML) lets you send authentication and authorization data between affiliated but unrelated web services. You can log in to Salesforce from a client app. Salesforce enables federated authentication for your org automatically.
Delegated authentication SSO integrates Salesforce with an authentication method that you choose. You can integrate authentication with your LDAP (Lightweight Directory Access Protocol) server or use a token instead of a password for authentication. You manage delegated authentication at the permission level, not at the org level, giving you more flexibility. With permissions, you can require some to use delegated authentication while others use their Salesforce-managed password.
Authentication providers let your users log in to your Salesforce org using their login credentials from an external service provider. Salesforce supports the OpenID Connect protocol, which lets users log in from any OpenID Connect provider, such as Google, PayPal, and LinkedIn. When an authentication provider is enabled, Salesforce doesn’t validate a user’s password. Instead, Salesforce uses the user’s login credentials from the external service provider to establish authentication credentials.