Do not let your CDN betray you: Use Subresource Integrity
This could also be used to remove the need for a CDN for common libraries like jquery and similar resources. If the browser knows it has a file in its cache with the same properties (has, size, name) even if it come from a different site it can be pretty sure that the content is the same so no new request is needed.So your site could use the cached copy of jquery (for instance) that was originally brought down to serve my site, or vice versa.