Trying to press a button on an internet page using vba

I know there is a similar question to this - but it doesn't show enough detail to help me, I am still new to this and need a little more guidance. What I am trying to do is use a VBA Macro to press a button on a web page.

The details that I can find out about the button are

class = "urBtnEmph"
id = "b1_pki"
ct= "Button"
onclick  = "LoginViaPKI();"

It isn't a page I have written, or have access to change anything on. But is there anyway I can automate clicking the button?

Thank You