Enable CORS by default in the nginx file

Enable CORS in the nginx file used by Docker.

nginx.conf

@@ -19,6 +19,31 @@ http {
     location / {
       root            html;
       index           index.html index.htm;
+      if ($request_method = 'OPTIONS') {
+          add_header 'Access-Control-Allow-Origin' '*';
+          add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
+          #
+          # Custom headers and headers various browsers *should* be OK with but aren't
+          #
+          add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
+          #
+          # Tell client that this pre-flight info is valid for 20 days
+          #
+          add_header 'Access-Control-Max-Age' 1728000;
+          add_header 'Content-Type' 'text/plain charset=UTF-8';
+          add_header 'Content-Length' 0;
+          return 204;
+      }
+      if ($request_method = 'POST') {
+          add_header 'Access-Control-Allow-Origin' '*';
+          add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
+          add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
+      }
+      if ($request_method = 'GET') {
+          add_header 'Access-Control-Allow-Origin' '*';
+          add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
+          add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
+      }
     }
   }
-}
+}