takeOverLogin (false): Take over the main login action. If takeOverLogin is
set, anytime the standard username/password login form would be shown,
a CAS login will be done instead.
+user_whitelist (null): Only allow login via CAS for users listed in this
+ array. This is useful when both CAS and password authentication is enabled
+ and there is a mismatch between some GNU social account names and CAS user
+ names. This prevents CAS users from logging in as someone else on GNU
+ social. When set to null, no CAS logins are filtered by this feature.
* required
default values are in (parenthesis)