Google Maps through proxy server with NGINX - google-maps

Question

I am trying to install an Angular application which uses google maps in a very restricted intranet. I have access to Google Maps through my server (which serves my app using NGINX), but not from my client. So those are the steps I took so far.
1 - I set the server IP for maps.googleapis.com in my /etc/hosts file in the client.
2 - I set the google maps IP in my /etc/hosts file in the server.
3 - I created a conf file so Nginx knows it needs to proxy pass this domain:
server{
listen 80;
server_name maps.googleapis.com;
location/ {
proxy_pass http://216.58.212.10/$uri$is_args$args;
proxy_set_header Host $host:$server_port;
}
}
I can download the first google maps api request:
http://maps.googleapis.com/maps/api/js?v=3.exp&libraries=visualization&sensor=false&callback=onGoogleReady
But when it tries to download this one:
http://maps.googleapis.com/maps/api/js/ViewportInfoService.GetViewportInfo?1m6&1m2&1d38.48493576049805&2d-9.36532974243164&2m2&1d38.97382736206055&2d-8.891716003417969&2u12&4sen-US&5e0&6sm%40366000000&7b0&8e0&callback=_xdc_._kxuspe&token=52829
It shows me this error:
The Google Maps Javascript must be downloaded directly from Google's servers.
Am I missing something here? Did anybody do that before? An more importantly: is it possible?