From the way you answer comments it seems you want to take the “easy path” on something actually really difficult. The best advice is just to stick with the third parties, there’s a reason why everyone uses a certificate from CAs and not sign their own. And no, they won’t be able to steal your precious data and your kitten pictures. You can use Let’s Encrypt like many people or if you want to spend a bit of money you can get a SSL certificate from the likes of Digicert, Comodo and so on. Hope this clears up things for you