Selective cross-realm authentication

A selective cross-realm authenticator associates an identifier with a request from an entity authenticated in one realm to access a resource associated with a second realm. The identifier indicates that the entity was authenticated in a realm other than the realm associated with the requested resource. A domain controller associated with the resource performs an access check to verify that the authenticated user is authorized to authenticate to the requested resource. Permissions associated with the resource can be used to specify levels of access to be granted to entities authenticated by a domain controller associated with another realm.