+If possible, the proxy should be configured to add CORS headers to its own error responses -- otherwise in-browser applications can't report proxy errors. For example, in nginx >= 1.7.5:
+
+<notextile><pre>
+server {
+ server_name keep.example.com
+ ...
+ add_header 'Access-Control-Allow-Methods' 'GET, HEAD, POST, PUT, OPTIONS' always
+ add_header 'Access-Control-Allow-Origin' '*' always
+ add_header 'Access-Control-Allow-Headers' 'Authorization, Content-Length, Content-Type, X-Keep-Desired-Replicas' always
+ add_header 'Access-Control-Max-Age' '86486400' always
+}
+</pre></notextile>
+
+*Warning:* Make sure you don't inadvertently add CORS headers for services _other than keepproxy_ while you're doing this.
+