In API v2 ssh_keys_controller in :index and :show method the 'user_id' parameter is documented as not required.

https://github.com/theforeman/foreman/blob/develop/app/controllers/api/v2/ssh_keys_controller.rb#L12
https://github.com/theforeman/foreman/blob/develop/app/controllers/api/v2/ssh_keys_controller.rb#L21

param :user_id, String, :desc => N_("ID of the user")

It is part of the resource URL and needs to be required. Wrong documentation leads to problems with parameter resolving in Hammer CLI.

hammer user ssh-keys delete --user admin --name test
Could not delete the SSH Key:
  missing param 'user_id' in parameters