...
Add class file name cas.am.CASAMLoginModule to "Pluggable Auth Modules Classes"
Click on Save button to save the changes in console.
*Alternate way:
Login to Access Manager Console as amadmin, using the URL: http://<host>.<domain>:<port>/amconsole.
Click "Service Configuration" tab.
Select "Core" under "Authentication Modules".
Add class file name cas.am.CASAMLoginModule to "Pluggable Authentication Modules Classes"
Click on Save button to save the changes in console.
...