Let me explain to you my situation:
As a member of an organization I have to be able to complete a form on site A and when I redirect the user to website B he should be able to login with the same credentials.
I have to mention that website B dose`t have any API or point of access.
So I have been thinking what if I create an identical form in site A and then open site B in a iframe and complete the same information into the inputs and then POST it.
Why I`m writing this its because I have been reading about same-origin-policy and this tells me that my solution won't work. I have also been reading through this page
What do you think? How would you tackle this?