[Koha] Secure 856u

hi i uploaded some fulltext PDF on koha and insert url in 856u to access , when i click 856u downloaded fulltext without user account, i changed authnotrequired => 1 to => 0 in perl but opac-detail in all records required ID and password , any way to secure only filed 856u or secure the records has contains 856u to access from my patrons only. thank's