Allow Stash create a new branch with alphanumeric and huphen characters only

We're using an external pre-receive hook to trigger our own perl script. In this script we have rule:
If user create a branch and push it to remote where branch name not match pattern (only alphanumeric, hyphen and underscore characters) the hook reject push.
Right now we have a problem: If user create a branch from Stash GUI, the plugin allowed create new branch without any allowed characters rule. After user clone repo and push that branch to remote repo, the hook reject push.

How we can set pattern for branch name in Stash?

I thinking about create a new plug-ins to listening BranchCreatedEvent. If new branch name not match pattern, we'll cancel it.

Please, give me a clue if I'm on right way.
Do you know how I can resolve this problem in other way?