What is federation and how does it enable cross-organization authentication?

Federation is an identity management model where multiple organizations agree to trust each other's authentication, allowing users to access resources across organizational boundaries using their home credentials. A user authenticated by their employer can access a partner organization's application without creating a separate account. Federation relies on protocols like Security Assertion Markup Language, or SAML, OpenID Connect, and OAuth. The identity provider authenticates the user and issues assertions that the service provider trusts.