It would be something custom developed, unless you find a similar solution that already meets your needs; I haven’t searched for one.
The general idea would be this: A user connects to a service (which could be just about anything; a RESTful API would probably be the current preference) and authenticates, selects a script to execute, and passes any necessary parameters to the server. The server side determines whether the user is authorized to run the script, and if so, loads up the credentials that have been stored for that particular script and executes it with the user’s parameters. Any output from the script would be passed back to the user (via XML or JSON in a REST API, most likely.)