You can't use SSO with Safari & Mac.To bypass autentication popup, You can make new identity and add Safari to user-agent field and choose exempt from authentication for this identity.
Are You using IronPort URL Filters or Cisco IronPort Web Usage Controls.I'm using Cisco IronPort Web Usage Controlsand it shows:IW_csec,-,"Unknown","-","Unknown","Unknown","-","-",462.00,0,-,"-","-">Seems Your does not handle categorization and skips...