73
Here's the SAML document that the Airline service receives
<AuthnRequest xmlns="urn:oasis:names:tc:SAML:2.0:protocol"
                           ForceAuthn="true"
                           ProviderName="CarRentalInc.com"
                           ID="abe567de6"
                           Version="2.0"
                           IssueInstant="2005-01-31T11:58:00Z"
                           Destination="https://www.AirlineInc.com"/>
Notice that there is no <Subject> element. If no <Subject> element is present in an AuthnRequest then it is implied that the Subject is the presenter of the AuthnRequest.