A nice project called „Custom Login Page“ has been published on OpenNTF.
The database is based on the domcfg5.ntf template and provides much more options to customize your login pages and error messages.
One use case could be to provide an alternative login screen in case of SPNEGO login failures. By default, you get only an error message and users don’t have the possbility to login with username and password instead of SPNEGO logon.
See more details and download on openntf.org