To configure a proxy server on a Windows device system wide, these are the current recommended registry keys

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings]
"ProxyEnable"=dword:00000001
"ProxyServer"="<fully qualified domain name of proxy>:<port>"
"ProxyOverride"="<*.domain.ext>;<*domain2.ext>;<ip.ad.dr.ess>;<local>"

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\CurrentVersion\Internet Settings]
"ProxySettingsPerUser"=dword:00000000