This page is heavily based on the GitLab Jenkins plugin webpage and Slack administration page.
This will be used as authentification. The channel can be changed within the jenkins job.
A Slack message can be sent at any stage of the Jenkins pipeline script:
def message2 = "OAI " + JOB_NAME + " build (" + BUILD_ID + "): passed (" + BUILD_URL + ") -- MergeRequest #" + env.gitlabMergeRequestIid + " (" + env.gitlabMergeRequestTitle + ")"
slackSend channel: 'ci-enb', color: 'good', message: message2