Currently, only per-application keys are available. If users had API keys, and the platform of their choice supports TCIA API, they would be able to access both public and access-restricted data from one familiar place.
API access to restricted collections is imminent. We have the capabilities in place and just need to finish documentation and testing so we can roll it out to the community. If you'd like to help us beta test please contact me and/or the helpdesk.