I am using McAfee Webgateway Cloud and I am currently having problems with Apples Software Update. Somehow when using McAfee Web Gateways proxy server, I cannot install any updates. Its asks for a username and password, but when installing it pops up with the error "Update Corrupt". This is defintley the proxy server. I have tried unblocking everything from the McAfee SaaS console with no luck. Please help! The updates are only successful when not using the proxy server which is not an option I can take.
Did you try bypassing entry *apple.com* from SSL inspection and check?
Try creating a rule on top of your policy using criteria Client.IP equals 18.104.22.168 ( This should be changed with IP Address of the actual problematic device) and set action as Stop Cycle and then try and see the results of updates.