How to fix iOS 12 Safari Cors preflight error?

Question

I am trying to understand CORs a little better as several users of our web app are complaining since they upgraded to iOS 12 they are receiving preflight errors.

The

Answer 1

I've been fighting with this exact same issue for the last two days and just now found the solution/answer.

It's a bug in iOSv12, but it's already fixed in iOSv12.1 beta (16B5059d), assuming the current beta code makes it into production.

The problem is that iOSv12 WebKit preflight OPTIONS calls don't leave the device. I've run WireShark and the iOSv12 simulator to confirm this.

Long time lurker, I made an account just to post this answer. If I broke rules/etiquette with this answer, I'm sorry.