StartSSL indeed offers free Class1 certificates for any subdomain
Posted by jpluimers on 2015/11/20
StartSSL does in fact offer free SSL certs for subdomains, though they are Class 1 certificates.
It works: just start the process for the domain, then when you get to the step for entering a subdomain, enter any one (of course
www works, but you can do the process multiple times so register certificates for multiple subdomains).