Hello Manil,
registration works just like normal:
you use the Gateway to identify the user, so if the user is stored on the internal IDP of the Gateway then you use the Gateway but in case of LDAP, SAML, or OAUTH, then you manage the user on those federal platforms, not via the Portal or Gateway, so the users would register not on the Portal but on the IdP
Maurizio Garzelli
Services Architect
CA Technologies
Office: +31611025636/ 20374 | Maurizio.Garzelli@ca.com<mailto:Maurizio.Garzelli@ca.com>