title: What is the purpose of SAML 2 Subject Name Identifier?
body: <p>When doing authn against a SAML 2 IdP, what does the Subject Name Identifier supposed to be for? Does it track each user login?</p>
  
  <p>I'm wondering if my SAML 2 service provider application should track these for different users. Since they are transient, they can be different for different logins (so I would need to track using a collection hanging off the user account).</p>