Adding a remote Helm repository without a default index file results in a 404

When trying to create a remote repo with a URL to a repository that does not have a default index file defined, the Test connection fails with a 404.
Example for such a Helm repository: https://cloudfoundry.github.io/stratos/
If I Save & Finish, the repository is created successfully and once put in a virtual repository, functions as expected.

Origin: https://stackoverflow.com/q/60675538/1300730

Update (May 21st, 2020) from another user:
I have faced the same issue as the guy on SO question, and found that in my case the remote repo does not function as expected. The repository I have doesn’t have default index, as the repository in question. The difference is: my remote repository requires authentication. And although I provide valid username and password, it does not work.