Let’s Encrypt is a free, automated, and open certificate authority (CA), run for the public’s benefit. It is a service provided by the Internet Security Research Group (ISRG).
Let's Encrypt certificate is valid for 90 days.
How to request the certificate: enter your e-mail address and domain name, chose the domain challenge verification method (HTTP or DNS), and then prove the challenge. After finishing the challenge, the certificate will automatically be generated!