the cert error is implying that somewhere you have a redirect to 10.100.12.1, but the cert (as it shows) in the controller has a CN=securelogin.arubanetworks.com
please replace any usage of http(s)://10.100.12.1 on your external cp with http(s)://securelogin.arubanetworks.com
having said this, https is always going to complain when a client tries to connect to https://google.com and it gets back a redirect to https://securelogin.arubantworks.com -- but that is a slightly different issue than the one you appear to have here.
note that a client will always receive a spoofed DNS response for securelogin.arubanetworks.com for the switch IP of the controller it is connected to - you do not need to put that in your DNS
regards
-jeff