docs: def install_key(self, keyfile, authorized_keys):
          """Install a key into the authorized_keys file."""
  
          # Make the directory containing the authorized_keys
          # file, if it doesn't exist. (Typically ~/.ssh).
          # Ignore errors; we'll fail shortly if we can't
          # create the authkeys file.
          try:
              os.makedirs(os.path.dirname(authorized_keys), 0o700)
          except OSError:
              pass
  
          keydata = open(keyfile).read()
          target_fd = os.open(authorized_keys, os.O_RDWR | os.O_CREAT, 0o600)
          self.install_key_data(keydata, os.fdopen(target_fd, 'w+'))