code: func (u *UserCommand) List(client auth.ClientI) error {
  	users, err := client.GetUsers()
  	if err != nil {
  		return trace.Wrap(err)
  	}
  	if u.format == teleport.Text {
  		if len(users) == 0 {
  			fmt.Println("No users found")
  			return nil
  		}
  		t := asciitable.MakeTable([]string{"User", "Allowed logins"})
  		for _, u := range users {
  			logins, _ := u.GetTraits()[teleport.TraitLogins]
  			t.AddRow([]string{u.GetName(), strings.Join(logins, ",")})
  		}
  		fmt.Println(t.AsBuffer().String())
  	} else {
  		out, err := json.MarshalIndent(users, "", "  ")
  		if err != nil {
  			return trace.Wrap(err, "failed to marshal users")
  		}
  		fmt.Printf(string(out))
  	}
  	return nil
  }
docs: // List prints all existing user accounts