Website: https://letsencrypt.org/

Let’s Encrypt is a new Certificate Authority: It’s free, automated, and open.

>>>> ACME: https://webencrypt.org/acme/

Certbot, previously the Let's Encrypt Client, is EFF's tool to obtain certs from Let's Encrypt, and (optionally) auto-enable HTTPS on your server. It can also act as a client for any other CA that uses the ACME protocol.

Certbot Official site: https://certbot.eff.org/
Get Certbot from: https://github.com/certbot/certbot 

Install

CentOS 6

sudo yum install epel-release

$ wget https://dl.eff.org/certbot-auto
$ chmod a+x certbot-auto

CentOS 7

yum install epel-release

yum install certbot

Cert

certbot[-auto] certonly

certbot[-auto] certonly --standalone -d example.com -d www.example.com

Wildcard

$ certbot certonly  \
 -d *.example.com \
 -d example.com \
 --manual \
 --preferred-challenges dns \
 --server https://acme-v02.api.letsencrypt.org/directory 

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NOTE: The IP of this machine will be publicly logged as having requested this
certificate. If you're running certbot in manual mode on a machine that is not
your server, please ensure you're okay with that.

Are you OK with your IP being logged?
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(Y)es/(N)o: Y

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Please deploy a DNS TXT record under the name
_acme-challenge.example.com with the following value:

UUN3Xf4jat9SWh_YssVK36P8EHa****************

Before continuing, verify the record is deployed.
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Press Enter to Continue

Renew

certbot[-auto] renew [--dry-run] [--quiet]

• https://github.com/Neilpang/acme.sh  - An ACME Shell script: acme.sh
• https://github.com/diafygi/acme-tiny  - A tiny script to issue and renew TLS certs from Let's Encrypt

1. https://certbot.eff.org/docs/
2. https://www.digitalocean.com/community/tutorials/how-to-secure-nginx-with-let-s-encrypt-on-centos-7 - How To Secure Nginx with Let's Encrypt on CentOS 7
3. https://blog.frognew.com/2018/07/lets-encrypt-wildcard-certificates.html - 更换博客HTTPS证书为Let's Encrypt的通配证书