[otrs] RADIUS & LDAP/DB

Hi, I would like to use RADIUS in order to authenthicate my customer users in my OTRS. Have I to create them in otrs before they try to access by customer users web interface? Is there a method to populate my cutomer users db dinamically when a customer users log on? This because I don't want to create a copy/direct link to my LDAP Thank you very much, Alessandro