The subject in a SAML 2.0 Assertion.
This is part of the ExSaml.Assertion struct. The name field in this struct should not
be used in any UI directly. It might be a temporary randomly generated
ID from IdP. ExSaml internally uses this to deal with IdP initiated logout requests.
If an authentication request was sent from ExSaml (SP initiated), the SAML response
is expected to include the original request ID. This ID is made available in
ExSaml.Subject.in_response_to.
If the authentication request originated from the IDP (IDP initiated), there won't
be a ExSaml request ID associated with it. The ExSaml.Subject.in_response_to
will be an empty string in that case.