Enforce HTTPS when behind a reverse proxy (Docker)

I'm running GitLab with the provided Dockerfile from: https://gitlab.com/gitlab-org/gitlab-ce/tree/master/docker The gitlab.rb says

# External URL should be your Docker instance.
# By default, this example is the "standard" boot2docker IP.
# Always use port 80 here to force the internal nginx to bind port 80,
# even if you intend to use another port in Docker.

So I'm running GitLab over HTTP internally but have placed another nginx instance in front of Docker which does the SSL termination.

So GitLab itself thinks it runs over HTTP I guess. When I'm in the overview of my projects I get HTTP and not HTTPS clone links and also Gravatar included links are HTTP.

Is there a way to force GitLab to use HTTPS links even when running behind a reverse proxy?