We call it ['Cache Refresh'](http://www.gluu.org/docs/admin-guide/oxTrust/configuration/#cache-refresh).
Gluu Server has a full [ldap tree] (http://www.gluu.org/docs/admin-guide/oxTrust/configuration/#attributes) inside where we are providing all OASIS standard ( https://wiki.oasis-open.org/security/SstcSaml2AttributeX500Profile ) and InCommon supported attributes.
During 'Cache Refresh', we do a mapping from Gluu Server's LDAP to customer's backend AD/LDAP. Mapping take place in such a way:
* Gluu Server's 'mail' ( urn:oid:0.9.2342.19200300.100.1.3 ) map to customer's backend email_address / mail attribute.
If there is any custom attribute required by organization, we can create it from Gluu Server's GUI [aka. oxTrust](http://www.gluu.org/docs/admin-guide/saml/outbound-saml/#ldap-attributes)