Which of the following is the BEST identity-as-a-service (IDaaS) solution for validating users?

LDAP is a directory access protocol typically used for on-premises directory queries and is not a cloud-based IDaaS solution for validating users.

Security Assertion Markup Language (SAML) is an XML-based open standard specifically designed for exchanging authentication and authorization assertions between an identity provider (IdP) and a service provider (SP). It is the foundational protocol used by most IDaaS platforms to validate user identities across cloud services through federated authentication. SAML directly addresses user validation by providing secure, standardized identity assertions in cloud-based identity scenarios.

SSO is a user experience concept that allows access to multiple applications with one login, but it is not itself an identity validation protocol-it relies on underlying protocols like SAML to perform actual authentication.

OAuth is an authorization framework designed to grant third-party applications limited access to resources, but it is not primarily designed for authenticating (validating) user identity.