The correct answer is SAML.

SAML is an XML based federation standard that defines a specific assertion format and the protocols to exchange identity and authentication information between an identity provider and a service provider. The SAML assertion itself is encoded in XML and carries elements for the subject authentication event and attribute statements that convey user identity.

SAML is widely used for enterprise single sign on and federated authentication where a trusted identity provider issues assertions to relying parties. While newer systems may use other token formats for APIs, SAML remains the common choice for browser based federated SSO in many deployments.

The JSON option is incorrect because JSON is a generic data interchange format and it is not the named federation protocol that transmits identity assertions in classic enterprise SSO. Modern alternatives such as OpenID Connect use JSON and JWTs for tokens, but that is a different standard.

The HTML option is incorrect because HTML is a markup language for rendering web content and it is not the encoding used to represent identity assertions. Browsers may carry assertions inside form posts or redirects, but the assertion format itself is not HTML.

The XML option is misleading because XML is the underlying encoding used by SAML but it is not the specific federation protocol. Saying only XML omits the standardized assertion structure and protocol behaviors that SAML defines.

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