The content of each cookbook is published on Gitlab Pages, to which only members of the TU Cookbooks gitlab members have access. The URL for your gitlab pages can be seen on your gitlab project main page.
Once you would you like to make your content public (world readable), you can change the visibility of gitlab pages. Navigate to Settings -> General -> Visibility and select Everyone in the Pages section.
Note that the jupyter notebooks to be run in binder will always need authentication to prevent resource abuse.