I have found this thread (this comment sumarizes it) explaining how to use draw.io together with a private gitlab by authorizing the application. In my company that option is not available.I think it could be possible to give draw.io access to the private gitlab by using access tokens but I don't know how.
It is okey if it requires some changes to the source code, as anyways we will be building it and deploying it in a private server.
So far I tried to do basically the same process but changing the gitlab-id parameter from the application-id to the access-token, that didn't work. Any ideas? Thanks!