Issue Summary

Jira sets the Vary header as `User-Agent` instead of `Accept-Encoding` for gzip requests.

Steps to Reproduce

Observe the `Vary` header in HTTP responses for gzip enabled requests.

Expected Results

Using `Accept-Encoding` is the more appropriate response header here. This was previously needed to support Internet Explorer.

Actual Results

`User-Agent` is less optimal for performance and cache management. 

Workaround

Customers can set `Accept-Encoding` in their proxy to override this.