Koding using OAuth when Gitlab uses SSL

I am trying to get koding to work with gitlab for one day now.
Since I did not know about koding.com before, I think that gitlab+koding together allow amazing things (like ease of teaching at university) and I love the new gitlab 8.11 release (also the issue board is more than "just great").

So the thing I am struggling with is that I can not get koding and gitlab work together using OAuth/SingleSignOn.
I am not sure if the problem is related to koding, gitlab or both. I hope that this is not the completely wrong place (or if so, maybe this can be moved)...

Let's describe my problem....
... I followed the instructions at https://gitlab.myserver.com/help/administration/integration/koding and my first problems dissapeared after I noticed the "--gitlabHost" parameter in the docker-compose.yml file used by koding. Now my problem is that when I click the "Enable Gitlab integration" in koding I get redirected to gitlab, but gitlab only shows the error "The redirect URI included is not valid."

After double-checking my OAuth application callback URL, I noticed that koding.com uses "http://gitlab.myserver.com/...." while the URL stored in gitlab's application settings starts with "https://gitlab.myserver.com/....". I guess this is the reason for my problem, but I can not seem to find the solution. Does gitlab's integration with koding require me to run gitlab on HTTP??

Also my koding settings seem to be correct, since in the docker-composer.yml file I double checked the parameters " --gitlabHost, --gitlabPort, --gitlabToken, gitlabAppId and --gitlabAppSecret". Shouldn't the redirect URL always use HTTPS if the gitlabPort is set to 443 (or is there some undocumented parameter like "--gitlabProtocol")??