To prevent opaque cache files, now all the CDN files will be requested in 'cors' mode if the cdn_cors_enabled global setting is enabled. Before enabling the setting, should enable the cors in the CDN server by adding the response header `access-control-allow-origin: *` or `access-control-allow-origin: https://discourse.example.com.`
And other external file requests other than CDN will not be cached if the response type is opaque.
