Validating the source code of the page
I found the attached answer.
Problems can be found even just looking at the page.
For instance, "Data mapping" is centered but all the other label are left aligned (see attachment).
For instance, fieldset are not used
For instance, colspan is greater than the number of columns of the table (see attachment)
Actually, the code in auth_config.php, is quite unusual in moodle 2.3, 2.4 and HEAD