mattermost-plugin-jira 
This plugin will create a webhook that your JIRA server can use to post messages to Mattermost when issues are created:
Installation
Go to the GitHub releases tab and download the latest release for your server architecture. You can upload this file in the Mattermost system console to install the plugin.
Developing
Run make vendor to install dependencies, then develop like any other Go project: Hack away and use go test, go build, etc.
If you want to create a fully bundled plugin that will run on a local server, you can use make mattermost-jira-plugin.tar.gz.
Releasing
To make a release, update the version number in plugin.yaml, and create a release via the GitHub interface. Travis will upload the distributables for you.