Need help developing plugin to customize S3 meta

I’m still pretty new to Ruby, and I’ve tried pouring through Discourse plugins on Github for guidance on modifying code in Discourse’s core code, but I’m a little overwhelmed with the complexity. I believe that a plugin to achieve what I’m after would be pretty simple, I just need some direction.

I’m trying to change the meta parameters of files uploaded to S3 from Discourse. Here’s where I’m looking:

In options, I simply need to change acl to private, and add a cache-control parameter. If you could help me get this code started, I’d really appreciate it. Seeing it in context, I think I’ll be able to understand how to extend other parts of the code for future plugins I develop.

Thank you!