Let’s Encrypt will release wildcard SSL certificate support in January 2018. This will ease the burden of adopting and deploying SSL in cases where multiple subdomains need SSL support. From the official announcement on July 6, 2017:
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 our upcoming ACME v2 API endpoint. We will initially only support base domain validation via DNS for wildcard certificates, but may explore additional validation options over time. We encourage people to ask any questions they might have about wildcard certificate support on our community forums.
The Let’s Encrypt API simplifies automating the renewal and creation of SSL certificates. Last month Let’s Encrypt reached a milestone of issuing more than 100,000,000 certificates and wildcard certificates will be a significant step in achieving a “100% encrypted Web”.