The service up is currently disabled since it does not have any login function (which is intentional by the original author I think)
I guess it would be possible to add the SSO login and have a Oauth2 login for the web page but we would also need an API key to be able to use the tool in a script, e.g. with the pb script by tomasino
We could use long-lived Oauth tokens for that or we could make a page that sets an API key similar to what Opengist does, this is a random fixed string that you can remove or replace and there is only one key available at any given time for the user.
Or we could have a PAT similar to what Github does which is username/PAT as login and different apps can use different keys so that a limited rights rules are possible (we don't need that for the upload service since there is only one function)
Or we could replace the tool completely if there is a similar tool that has Oauth support directly. I used a site before that used their own login and had an API key that could be provided as a POST parameter or a header, but I don't think that software was open source.
For now I will look into how this is possible with PHP, the script is pretty simple, it is actually one file, the Oauth will require composer, but that is not really a problem