Github now can automatically support HTTPS for the www subdomain alongside the root domain.
https://www.joshuafox.com shows an SSL certificate error, while the root domain is fine.
The DNS records seem correct, as shown by
Setting for Google Pages is as below.
The www subdomain is not mentioned there, and I think that it is supported (without HTTPS) simply with a CNAME DNS zone.
How do I enable HTTPS support for my www subdomain as well as for the root domain?