Dokku CORS SSL nginx template

nginx.conf.template

## This is/was the template from /root/dokku/plugins/nginx-vhosts/templates/nginx.ssl.conf
## See the CORS section added below
server {
  listen      [::]:80;
  listen      80;
  server_name $NOSSL_SERVER_NAME;
  return 301 https://$SSL_SERVER_NAME\$request_uri;
}

server {
  listen      [::]:443 ssl spdy;
  listen      443 ssl spdy;
  server_name $SSL_SERVER_NAME;
$SSL_DIRECTIVES

  keepalive_timeout   70;
  add_header          Alternate-Protocol  443:npn-spdy/2;
  location    / {

## Start CORS here.  See http://enable-cors.org/server_nginx.html for comments

    if (\$http_origin ~* (^https?://.*\.$VHOST$)) {
        set \$cors corson;
    }
    if (\$http_origin ~* (^http://(localhost|127.0.0.1)(:[0-9]+)?$)) {
        set \$cors corson;
    }

    if (\$request_method = OPTIONS) {
        set \$cors '\${cors}options';
    }

    if (\$request_method = GET) {
        set \$cors '\${cors}get';
    }
    if (\$request_method = POST) {
        set \$cors '\${cors}post';
    }

    if (\$cors = corsonget) {
        add_header Access-Control-Allow-Origin \$http_origin;
        add_header Access-Control-Allow-Credentials true;
    }

    if (\$cors = corsonpost) {
        add_header Access-Control-Allow-Origin \$http_origin;
        add_header Access-Control-Allow-Credentials true;
    }

    if (\$cors = corsonoptions) {
        add_header Access-Control-Allow-Origin \$http_origin;
        add_header Access-Control-Allow-Credentials true;

        add_header Access-Control-Max-Age 1728000;

        add_header Access-Control-Allow-Methods 'GET, POST, OPTIONS';
        
        add_header Access-Control-Allow-Headers 'Authorization,Content-Type,Accept,Origin,User-Agent,DNT,Cache-Control,X-Mx-ReqToken,Keep-Alive,X-Requested-With,If-Modified-Since';

        add_header Content-Length 0;
        add_header Content-Type 'text/plain charset=UTF-8';
        return 204;
    }
### End CORS

    proxy_pass  http://$APP;
    proxy_http_version 1.1;
    proxy_set_header Upgrade \$http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_set_header Host \$http_host;
    proxy_set_header X-Forwarded-Proto \$scheme;
    proxy_set_header X-Forwarded-For \$remote_addr;
    proxy_set_header X-Forwarded-Port \$server_port;
    proxy_set_header X-Request-Start \$msec;
  }
  include $DOKKU_ROOT/$APP/nginx.conf.d/*.conf;
}

A heads up for people who find this issue in the future: you can embed this and other NGINX configurations in nginx.conf.sigil in your app, and dokku will load it for you. Here's an example of a pretty open CORS + SSL template:

https://github.com/qrush/skyway/blob/master/nginx.conf.sigil

For thouse reading @qrush message in 2021 -> here is a working link to the same file https://github.com/qrush/skyway/blob/3d009fae3a801bc402650f5e9aa256fab718c7ab/nginx.conf.sigil