Cybersource Secure Acceptance

Hi All,
Has anyone successfully connected to Cybersource’s payment gateway using their Secure Acceptance option?
I am trying to connect using the api connector with a POST ACTION call.
Below are the fields provided:

I am getting error “403 - Forbidden”, stating that I am not authorized to view the page.
I am thinking the issue may be that I am not passing the secret key. I have tried all kinds of authentication methods to pass it on, but nothing works.
Searched all kinds of forums but to no avail. I am hoping someone on this forum has experimented with Cybersource.