[FEAT] host-specific ssh keys for cockpit container

[benniekiss]

This PR adds the ability to set host-specific ssh keys via env-var in the cockpit-ws container.

Users can pass environment variables in the format of COCKPIT_SSH_KEY_PATH_{HOSTNAME}, where HOSTNAME is the hostname used in the Connect to field of the cockpit login page, and cockpit will use the configured key to login to the host. If no host-specific key is set, it falls back to using the COCKPIT_SSH_KEY_PATH environment variable.

I still need to make a unit test, but I wanted to ask for suggestions as to the best route. The cockpit bastion test could be replicated, or it could be refactored to test host-specific keys. I wasn't sure what the best approach would be, and would appreciate any advice before proceeding!

This functionality will enable users to login to multiple hosts via ssh keys once the host-switcher is deprecated, providing a solution to user concerns such as #20901

[martinpitt]

Thanks @benniekiss ! This is a pretty cool feature! It does need an integration test, yes. I suggest you factorize that test a bit, with a do_test_key_login(options: str), and then call this several times in testKeyLogin() with the scenarios (only COCKPIT_SSH_KEY_PATH, the per-hostname ones, and the fallback). You can use invalid keys for the ones that you don't expect to get picked of course, so you don't need multiple VMs/SSH targets.

[benniekiss]

Thank you! I'll start working on the test soon.

FWIW, I've been running this patch personally, and it's worked well.