===== SP PrincipalNameMapping element

This element is optional.
When creating a Java Principal object that you obtain from methods like HttpServletRequest.getUserPrincipal(), you can define what name that is returned by the Principal.getName() method.
The `policy` attribute defines the policy used to populate this value.
The values are `FROM_NAME_ID`.
This policy just grabs whatever the SAML subject value is.
The other is `FROM_ATTRIBUTE`.
This will pull the value of Principal.getName() from one of the attributes in the SAML assertion received from the server.
The default value is `FROM_NAME_ID`.