Ask HN: What SaaS provides both back end and front end for logins and payments?

I want to spend as much time possible developing my core product and as little as possible developing the generic services around paying customers. I want not only the backend APIs but also white-labeled template/widget/iframe that I can drop to my HTML, including login/register/forget password forms and recurring payment forms. Also I want some BaaS solution to store data against those customers.