Transparent proxy on MacBook

Hello, I have been scratching my head about a pop up I keep getting which asks for my password. It's the one that says 'transparent network proxy for Apple system services wants to use the 'login' keychain'.

I have searched a lot to try to find out more, but usually the thread doesn't answer it fully, until today when I saw an answer to someone's question about this which asked 'is this a used Mac you bought?' - mine is, and so this leaves me wondering if it isn't a harmless thing utilised by the person I bought it from in order to set up the MacBook with OS etc.

Can anyone shed more light on this for me?

essentially I want to stop seeing the pop up, and if it might be harmful, remove the thing that's causing it.

All help gratefully received :)