WPF MVVM Toolkit add new button with async command

gistfile1.cs

in xaml
        <Button Content="Generate key" Command="{Binding GenerateKeyCommand}"/>

in viewmodel
    private IAsyncRelayCommand generateKeyCommand;
    public IAsyncRelayCommand GenerateKeyCommand => generateKeyCommand ??= new AsyncRelayCommand(GenerateKey);

    private Task GenerateKey()
    {
        MessageBox.Show("GenerateKey");
        return Task.CompletedTask;
    }