New install with Mediawiki 1.29 on Ubuntu 16.04 (PHP 7.0.18; apache2 2.4.18).
From Apache logs:
PHP Fatal error: Uncaught Exception: /var/www/wiki/extensions/LdapAuthentication/extension.json does not exist! in /var/www/wiki/includes/registration/ExtensionRegistry.php:99
The following is also a failure (similar to the "LDAP Authentication extention to registration not working" post):
/var/www/wiki# php maintenance/convertExtensionToRegistration.php extensions/LdapAuthentication/LdapAuthentication.php