$ bin/rails g authentication --help
Usage: rails [options]
-p port set the port (default is 4567)
-s server specify rack server/handler
-q turn on quiet mode (default is off)
-x turn on the mutex lock (default is off)
-e env set the environment (default is development)
-o addr set the host (default is (env == 'development' ? 'localhost' : '0.0.0.0'))
https://codewithrails.com/rails-authentication claims that the generator has a help option saying what's available. But it's not recognized by bin/rails. Witness: