Login Page - How to change?

Where can I change the login page to adopte to my own CI? I did not find anything in the docs nor in the source code. Magic?

What do you mean by CI?
You can modify the style of the login page using custom CSS. You can find more information here:

CI = corporate identity. Change the logos, add more information, change the color of the page and so on. Just to edit the html code of the page.

Exactly, that's what the LoginAppFolder is for. It's possible and actually was designed for that.
Use it to customize the logo, the CSS styles, among other things.