title: Configuring a Gitlab runner secret that is not visible to the repos using it
body: <p>I want to implement a SAST tool (with a docker image) on my Gitlab that is integrated with my vulnerability reporting dashboard, but I dont want any of the repos maintainer/dev to be able to access the docker secret_key besides in its intended flow.</p>
  <p>The flow should be like this:
  Gitlab Runner (+ docker secret key) -&gt; Docker image (contains SAST Tool + admin-level dashboard credential) -&gt; Code Vulnerability reporting dashboard</p>
  <p>I have considered several solutions (eg making the dashboard credential unique for each repos and making it supplied from the user instead of being saved in the docker image), but it requires either considerable maintenance effort or somehow enabling the repos maintainer to get the info.</p>