To migrate users in advance would require custom development.
However, internally mojoPortal uses its own database user objects even when using ldap authentication. Upon successful ldap authentication a mojoPortal user will be automatically created in the database if he doesn't already exist, so technically it is not required to migrate or import data ahead of time if the user has an AD/Ldap account, he will be able to login right away without any migration.
Best,
Joe