how can we secure our wan ip and port to be used by some other peoples via proxy

Are you saying you want to avoid your web proxy being used by out side world?
Assuming that's whats your asking, I have to say, I'm concern that why is it already possible in your router? you should block all unnecessary input packets. and only allow those that you need, not the other way around.
Anyway, you have two options for that, first by blocking the port for incoming packets from your wan interface:
in-interface value, should be your wan interface name, so edit it if its required. and dst-port, should point to your web proxy port, which is by default 8080. again, edit it if its required.

The other way would be to use the access function in web proxy itself. assuming your local network subnet is 192.168.0.0/24, you could deny all other source addresses:
I strongly recommend using the first method.

Thinking again, you might be asking how you could give access to some people from wan to your web proxy. well, if they are using static ip's, you could simply allow those ip's to access to the port and drop others.