It seems that as of a few months ago, two popular (unofficial) command line clients for ACD (Amazon Cloud drive) were acd-cli[1] and rclone[2], both of which are open source. Importantly the ACD API is OAuth based, and these two programs took different approaches to managing their OAuth app credentials. acd-cli's author provided an app on GCE that managed the app credentials and performed the auth. rclone on the other hand embedded the credentials into their source, and did the oauth dance through a local server.
On April 15th someone reported an issue on acd-cli titled "Not my file"[3] in a user alleged that they had received someone else's file from using the tool. The author refered them to amazon support. The issue was updated again on May 13th with another user that had the same problem - this time with better documentation. The user reached out to security@amazon.com to report the issue.
Amazon's security team determined that their system was not at fault, but pointed out a race condition in the source for the acd-cli auth server (sharing the auth state in a global variable between requests...) and disabled the acd-cli app access to protect customers.[4]
In response to this banning, one user suggested that a workaround to get acd-cli working again would be to use the developer option for local oauth dance, and use rclone's credentials (from the public rclone source).[5] This got rclone's credentials banned as well,[6] presumably when the amazon team noticed that they were publicly available.
To top this all off, the ACD team also closed down API registration for new apps around this time (which seems to have already been a strenuous process). I suppose the moral of the story is that OAuth is hard.
[1]: https://github.com/yadayada/acd_cli [2]: https://github.com/ncw/rclone [3]: https://github.com/yadayada/acd_cli/issues/549 [4]: https://github.com/yadayada/acd_cli/pull/562#issuecomment-30... [5]: https://github.com/yadayada/acd_cli/pull/562#issuecomment-30... [6]: https://forum.rclone.org/t/rclone-has-been-banned-from-amazo...