The new project was progressing rapidly until I hit a difficult-to-understand CORS issue in Safari. This post documents the specific issue and how I resolved it. I like to say that when I encounter issues that I can’t resolve in a few hours, it’s a really obscure issue. This issue took me over 24 hours to fully understand & then resolve. Scenario The service takes incoming file assets from a member, posts them to a member-private location in S3, performs a transformation on the asset, then makes that transformation available to the member by delivering it back into a browser session upon request.