Question

Could I add some custom control to the standard Message Box for read input value, for example text fields for user name and password, or I should create custom winform with "Ok,Cancel" buttons and text fields?

Related: Which control to use for quick text input (inputbox)?

Answer 1

Create your own.

Creating a custom modal (or otherwise) input dialog isn’t all that difficult and you can built the extensibility you need for reuse.

public class ValueHolder {
    public string SomeInput { get; set; }
    public DialogResult Result { get; set; }
}

public class GimmeValues : Form {
    //... HAS A TEXTBOX and Okay Buttons...

    private GimmeValues() {        
        okButton.DialogResult = DialogResult.OK;
        cancelButton.DialogResult = DialogResult.Cancel;
        // ... other stuff
    }

    public static ValueHolder GetInput(IWin32Window owner) {
        using (GimmeValues values = new GimmeValues()) {
            DialogResult result = values.ShowDialog(owner);
            return new ValueHolder { 
                SomeInput = values.Textbox1.Text,
                Result = result
            };
        }
    }
}

Okay I just wrote that all in this editor so forgive any syntax mistakes.
You could do something like the above but clean it up a little, add the extensibility you need (in terms of buttons and inputs showing that you need etc)… then just call it like ValueHolder value = GimmeValues.GetInput(this); where this would represent an IWin32Window…

The resulting value of value would be the selected nonsense and you could perform your logic..

if(value.Result == DialogResult.OK && !string.IsNullOrEmpty(value.SomeInput)){
    //TODO: Place logic....
}