Make your site a safe place. From January 2018 Let’s Encrypt will start issuing wildcard certificates. They are aimed to help you accelerating the web’s progress towards 100% HTTPS. Ease HTTPS deployment with wildcard certificate.
Let’s Encrypt is a free, automated and open certificate authority, run for the public’s benefit and provided by the Internet Security Research Group. They give digital certificates in order to enable HTTPS (SSL/TLS) for websites. Their mission, as they claim, is to get 100% encrypted web.
A wildcard certificate can secure any number of subdomains of a base domain (e.g. *.example.com). This allows administrators to use a single certificate and key pair for a domain and all of its subdomains, which can make HTTPS deployment significantly easier. Wildcard certificates will be offered free of charge via upcoming ACME v2 API endpoint. Let’s Encrypt will initially only support base domain validation via DNS for wildcard certificates, but may explore additional validation options over time.
If you want to receive such certificate, read more info on Let’s Encrypt site.