I think they did eventually. I remember trying to use Stripe for a project during college (2012ish) that involved building a website with a REST integration in C#. My rtfm'ing skills were much worse back then so I could be wrong, but yeah, you had to do a bunch of server-side implementation and make calls to their API. It seemed quite challenging to me at the time, but looking back, it really wasn't. They've gotten rid of that extra step now though. You can just drop in the javascript and their html form with api keys and you're ready to go.