Add custom parameters to Siebel Login Page

Greetings Siebel Guru's,

I have some requirement to pass an additional parameter to the login command and validate the same during Application Start event and if failed we need to log the user out of application.

As of now I can read that we can create custom fields on login page by modifying the Login Web Page of the application and add additional web page items to placeholders available in web template., but do we have any example in bookshelf to refer to.

FYR:

We have _SwePassword, _SweUserName as web page items and same exposed in Siebel Login Page.

I need to add a new field like AgentCode on login page and then use it in server side scripting.