Can a broker return an error and reject a commit?

I'm trying to find a way to make up for the fact that Bitbucket does not have the ability to require a JIRA id in the commit message. We are migrating from Atlassian's svn service and need/want this same functionality in Bitbucket.

It looks like brokers can look at the commit information. Can they exit with an error and prevent the commit from being accepted?

If so, then perhaps we could write a broker to ensure commit messages comply.