Login pop up

Hi there,

I would need to add to my website a login plugin. I have a variable product and once a customer has choosen his options and click on add to cart, I would like that a pop up opens with the possibility to either create an account(just by giving his email address), either connect himself if account already created. Once email wirtten, I would like to redirect the customer to the checkout page with the options selected before. How could I do?

Thanks,