How many certificates are needed if to redirect non-www requests to www prefixed ones over https

Question

If I want to redirect https://example.com to https://www.example.com, are two certificates needed? One is for example.com and the other for www.example.com?

Answer 1

Usually certificate authorities (CA) issue SSL certificate which is valid for both domain.com and www.domain.com. You should check with the CA if they do this (as I understand, most do).