Thank you for your answer.
I used the following workaround:
I tried to access the mysql-database which apparently is on another container and edited the customHeaders right there for the specific dataSet. At least I was able to access the API, but still my customHeaders get overwritten with an empty String if I save something in the edit-dialog, due to the missing input field.
You can use the following instructions to pull the release23 container:
run docker-compose down if the containers are up
Open the docker-compose.yml (or the cms_custom_ports.yml if you’re using that file to up your containers)
Find the line under cms-web that specifies the docker image that is used to pull cms files, it should look like this : image: xibosignage/xibo-cms:release-2.3.9
Change the image to release23 ie that line should be changed to: image: xibosignage/xibo-cms:release23
run docker-compose pull
run docker-compose up -d
You can then go to the Authentication tab and enter a comma separated string of custom HTTP headers here: