Need help with Client-Initiated Form SSO

Standard forms-based SSO doesn't work with a home-grown web app I am trying to get SSO working for. I've read through the manual page for APM for client-initiated forms. Following that manual I still can't get it to work. Below is the sequence for the web page on how you get to the POST of the forms.

1) GET

2) Response is a 302 to

3) The GET to results in a 302 to dynamic string here"

4) POST to dynamic string here" with forms for redirectUrl (blank value), userName, and password.

Below is my current config. I can't find a way to include the redirectUrl form parameter with a blank value. I'm not certain that is why it isn't working. I think that, combined with I don't know how to set this up to capture that dynamic string and pass that through as part of the request-value, is why it isn't working. As usual any help is much appreciated. My testing indicates that including that dynamic string is necessary.

forms {
    FormProfileName {
        controls {
            password {
                secure true
                value "%{session.sso.token.last.password}"
            }
            userName {
                secure true
                value "%{session.sso.token.last.username}"
            }
        }
        request-value https://www.webapp.org/abc/portal/connect/home/login/
        success-match-type url
        success-match-value /abc/myportal/connect/home/word/*
    }
}