RTC Sandbox connectivity

You have to first create a Sandbox via the Sandbox UI before being able to access anything. Then you should be able to access it in any way your Jazz repo permissions / process permissions allow.

https://jazz.net/sandbox

Yes, I understand how to access it via the UI, but I guess the answer to my question is no; one cannot access the sandbox repository via Java APIs.
For instance, this doesn't work:

ITeamRepository repository = TeamPlatform.getTeamRepositoryService().getTeamRepository("https://jazz.net/sandbox/rtc" );

repository.registerLoginHandler(new ITeamRepository.ILoginHandler() 

        {

            public ILoginInfo challenge(ITeamRepository repository) 

            {

                return new ILoginInfo() 

                {

                    public String getUserId() {"userName"}

                    public String getPassword() {"password"}

                };

            }

        });

repository.login(monitor);