Is it possible to have custom headers on Amazon S3 with arbitrary naming?
For example, I am using a CDN pointing to Amazon S3 as the origin server, and in order to enable advanced functionality on the CDN I need to use a custom header x-something-something…
I see it’s possible to do this with x-amz-meta-(something) but what about something more general like x-(something)-(something) without the amz?

I don’t think it is possible with their current API. They cover the major headers you will need for caching and browser interoperability.
I think they are being safe in only allowing
x-amz-meta-prefixed custom headers, possibly to keep from clashing with user selected headers when they update their api in the future.If you need custom attributes attached to your objects, it should be trivial to parse out the
x-amz-meta-in your client application.