Joyent did http request signing using ssh keys[0]. Their cli tools used this mechanism. There's been some effort to carry this forward through the standards process[1].

I'm not going to comment on whether this is a _good idea_. It is a clever way to leverage tools already available in dev environments to deploy API keys with encryption and hooked into your OS keyring (via the ssh-agent).

[0]: https://github.com/joyent/node-http-signature/blob/master/ht...

[1]: https://datatracker.ietf.org/doc/draft-cavage-http-signature...