You've installed the SimpleRisk Custom Authentication Extra and are trying to get Active Directory authentication to work, but every configuration you try just results in a blank page when authenticating with a valid AD user? Check in the Apache error log and you'll likely see a message like this:
[Mon Apr 24 09:42:16.330506 2017] [:error] [pid 12457] [client X.X.X.X:2482] PHP Fatal error: Call to undefined function ldap_connect() in /var/www/html/simplerisk/extras/authentication/index.php on line 508, referer: https://X.X.X.X/index.php
If you're seeing this, it is because the LDAP libraries for PHP have not yet been installed on your SimpleRisk system. Here's how to install the PHP LDAP library.
sudo apt-get install php5-ldap
sudo php5enmod ldap
sudo service apache2 restart