How to configure jetspeed 2 for yahoo (sample)

Login to Jetspeed as a specific user, select designing menu, and add portlet [SSO Web Content] and configure it as follows...

sso.type: form
sso.form.Credential: passwd
sso.form.Action: https://login.yahoo.co.jp/config/login
sso.form.Args: (blank)
SRC: http://finance.yahoo.co.jp/
sso.form.principal: login
SSO Principal: (email for yahoo)
SSO Credential: (password for yahoo)

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Regarding sso.form.Args, after some tries and errors, I understand that it doesn't need to describe about Cookies and session ID.

* Login Screen of JetSpeed










* Logged in and SSO Yahoo
I don't know why I am soon redirected to http://www.yahoo.co.jp/ just after login. After pressing [back] button of FireFox, I see the JetSpeed screen. There remains something I need to resolve.