In this mini howto I would like to show how to add a required captcha field in the login form, after a defined number of unsuccessfull attempts.
To do this, I will use the blog demo that you have in default Yii download package (path/to/yii/demos/blog).
This HowTo assumes that you have a smattering of ACL in general and of how the acl-extension works basically. It will introduce you into the abstract and give you a hint on how to use Business-Rules. If you have in-depth questions, please refer to the extension documentation.
Using ACL in an RBAC-manner cannot and should never obscure the fact that the underlying system is still ACL-based. In fact, the Business-Rules are just another layer in the permission-check plan.
To extend the functionality of you web application relative to your requirements you are supposed to use existing yii core libraries or use external libraries. There are some steps to ensure security, uniqueness, modularity, performance and to avoid rework in future.
I installed phpseclib because I needed to do some AES encryption in my project. After all the hassle of installing php lib, I found out that Yii already has a security module (securityManager). I finally decided to keep using phpseclib because it has one big advantage over Yii securityManager module, it does not requite mcrypt to be installed in the phpserver!