reject cross-origin websocket handshakes

Neither /ws nor the jsmpeg websockets checked Origin, and the internal port grants admin to everyone, so any page a LAN user visited could open ws://frigate:5000/ws and send commands or read streams. Both servers now reject a browser handshake whose Origin host matches neither Host nor X-Forwarded-Host, and allow handshakes without an Origin for non-browser clients. nginx now forwards an outer proxy's X-Forwarded-Host instead of overwriting it, so proxies that rewrite Host and the Home Assistant integration's proxy still match.

docker/main/rootfs/usr/local/nginx/conf/nginx.conf

@@ -54,6 +54,13 @@ http {
         default 1;
     }
 
+    # keep an outer proxy's X-Forwarded-Host so the websocket servers can
+    # match a browser's Origin when that proxy rewrites Host
+    map $http_x_forwarded_host $forwarded_host {
+        "" $http_host;
+        default $http_x_forwarded_host;
+    }
+
     upstream frigate_api {
         server 127.0.0.1:5001;
         keepalive 1024;

docker/main/rootfs/usr/local/nginx/conf/proxy.conf

@@ -4,7 +4,7 @@ proxy_set_header Upgrade $http_upgrade;
 proxy_set_header Connection "Upgrade";
 proxy_set_header X-Original-URL $request_uri;
 proxy_set_header X-Forwarded-Proto $scheme;
-proxy_set_header X-Forwarded-Host $http_host;
+proxy_set_header X-Forwarded-Host $forwarded_host;
 proxy_set_header X-Forwarded-URI $request_uri;
 proxy_set_header X-Forwarded-Ssl on;
 proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;