How to modify its default login interface in node-red?

I want to modify it into my own login interface. I don't know where it is.

When you say “change the default interface”, do you mean changing the look and feel visually, or allow different login methods. For the last one is builtin support through express-passport packages and/or custom code and configuration, for the first I don’t have a clue.

You can change the panel as part of the theme