If you need a free SSL certificate Let's Encrypt seems like the obvious way to go. But the installation and renewal process of Let's Encrypt surely has it's caveats. An alternative to Let's Encrypt is to use a free certificate issued by Cloudflare. On his blog Taylor Otwell published a post explaining how to request and install such a certificate.

I personally prefer to use Cloudflare, another service that offers free SSL certificates, as well as a variety of other free and paid services that are useful for web developers. I prefer Cloudflare because: - Cloudflare doesn’t require any renewal process to ever run on my server. LetsEncrypt renewals must run on my server at least every 3 months and that’s just one more thing that sometimes can (and does) go wrong. - Cloudflare supports wildcard sub-domains.

https://medium.com/@taylorotwell/free-wildcard-ssl-using-forge-cloudflare-ab0ebfbf129f