Using Redmine REST API to concurrently update Issues

Question

Hoping someone could shed some light as my searches have turned up very little information.

I want to use Redmine's REST API for Issues to do:

1. GET /issues/[id].json to get the content of a specific issue.
2. Make changes to the above content.
3. Finally PUT /issues/[id].json the content back.

But I want to perform this using some form of concurrency control (ideally optimistic locking), so that content isn't changed by someone else around 2, promptly followed by 3 destroying said change.

This link hints on such possibility:

• redmine.exceptions.ConflictError - (Why does this class exist?)

I'd assume there'd be some way of specifying a compare value, possibly updated_on, to do compare-and-swap-esk locking with PUT /issues/[id].json, but I can't find anything regarding this.

Redmine's web interface provides a concurrency control mechanism, so I'm stumped as to why there's so little information on this.