Restored nginx CORS configuration for credentials

LEARNER-568

playbooks/roles/credentials/templates/edx/app/nginx/sites-available/credentials.j2

@@ -15,6 +15,11 @@ upstream credentials_app_server {
 {% endfor %}
 }
 
+map $http_origin $cors_header {
+  default "";
+  '~*^https?://({{ CREDENTIALS_CORS_ORIGIN_WHITELIST|join('|')|replace('.', '\.') }})$' "$http_origin";
+}
+
 server {
   server_name {{ CREDENTIALS_HOSTNAME }};
 
@@ -38,7 +43,18 @@ server {
   }
 
   location ~ ^{{ CREDENTIALS_STATIC_URL }}(?P<file>.*) {
+    if ($request_method = 'OPTIONS') {
+      add_header 'Access-Control-Allow-Origin' "$cors_header";
+      add_header 'Access-Control-Allow-Methods' 'GET, POST';
+      add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';
+      add_header 'Access-Control-Max-Age' 1728000;
+      add_header 'Content-Type' 'text/plain charset=UTF-8';
+      add_header 'Content-Length' 0;
+      return 204;
+    }
+
     root {{ CREDENTIALS_STATIC_ROOT }};
+    add_header Cache-Control "max-age=31536000";
     try_files /$file =404;
   }