If a request Authenticated using cAuthenticationMode of UserSecurity you can access the user security object directly from here, with the appropriate user selected.

FUNCTION OnLoad()

IF !Process.Authenticate()
   RETURN
ENDIF

this.lblMessage.Text = this.cAuthenticatedUser + " " + ;
                this.oUserSecurity.oUser.Fullname)
ENDFUNC

o.oUserSecurity