https://marco.org/2009/01/11/now-that-ive-gone-through-the-process-of-getting
Now that I’ve gone through the process of getting my own SSL certificate, I know first-hand how easy it is. (It was also cheap: about $30 at GoDaddy.)
There’s absolutely no excuse to use a self-signed or invalid certificate in 2009. Don’t confuse your users and complicate the browsing experience (or your API usage) by making us dismiss the warnings or force our software to skip validation.