Setting up Single Sign-On Form-based client-initiated with 2 forms login page

Hello, I want to set up a Single Sign-on Form based client-initiated for an application that the login page has 2 forms that process the logon, for example:

I'm following the instructions outlined in link text without any success.

The farthest i have come with my setup is that the single sign-on works but leave me in a page that is not the user home page, in order to get there, i've to write the full URL in the browser address bar.

I created a wireshark capture when i clicked on the login button in the original login page (not the login page from APM, i mean the server login page) and it generates a POST method to /WebInterface/function/, and then a POST to /. When i clicked on the login button from APM, it generate just one POST, it is the POST to /, and it authenticate successfully, but i don't see the POST to /WebInterface/function/, that is why i've to write http://myhost.mydomain.com/WebInterface/function/ in order to get the user home page.

Do i have to custom the javascript injected? Can you help me how can i set up single sign-on for this kind of login page?, the examples i've reviewed just show single sign-on with one form.