s3stash is a tool provided by Cycle Computing to allow customers to share large files with us securely. Cycle Computing support provides s3stash builds for Linux and Windows on request. The executable has time-limited credentials built in.
s3stash --case <case number> <file1> [<file2> <...fileN>]
If your network requires a proxy setting for HTTP/HTTPS requests, use the --proxy flag. You will be prompted to enter a proxy in the form of http://username:email@example.com:port