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Get SSL Certificate (Let's Encrypt)
2021/02/23
 
Get SSL/TLS Certificates from Let's Encrypt who provides Free SSL/TLS Certificates.
Refer to the details for Let's Encrypt official site below.
⇒ https://letsencrypt.org/
The expiration date of a cert from Let's Encrypt is 90 days, so you must update within next 90 days later.
However, if you installed Certbot package from Snapd like follows, Systemd Timer script is included in it, so renewal is done automatically.
[1]
Install Snapd, refer to here.
The certbot-auto 1.10.0 and later are officially not recommended and also they are not updated,
certbot from Snapd is officially recommended to install to use.
[2] Install Certbot client from Snapd.
[root@dlp ~]#
snap install certbot --classic

certbot 1.12.0 from Certbot Project (certbot-eff✓) installed
[root@dlp ~]#
ln -s /snap/bin/certbot /usr/bin/certbot

[3] Get certificates.
It needs Web server like Apache httpd or Nginx must be runing on the server you work.
If no Web server is running, skip this section and Refer to [3] section.
Furthermore, it needs that it's possible to access from the Internet to your working server on port 80 because of verification from Let's Encrypt.
# for the option [--webroot], use a directory under the webroot on your server as a working temp

# -w [document root] -d [FQDN you'd like to get certs]

# FQDN (Fully Qualified Domain Name) : Hostname.Domainname
# if you'd like to get certs for more than 2 FQDNs, specify all like below

# ex : if get [srv.world] and [dlp.srv.world]

# ⇒ [-d srv.world -d dlp.srv.world]
[root@dlp ~]#
certbot certonly --webroot -w /var/www/html -d dlp.srv.world

Bootstrapping dependencies for RedHat-based OSes that will use Python3... (you can skip this with --no-bootstrap)
dnf is /usr/bin/dnf
dnf is hashed (/usr/bin/dnf)
.....
.....
# for only initial using, register your email address and agree to terms of use
# specify valid email address
Enter email address (used for urgent renewal and security notices) 
(Enter 'c' to cancel): root@mail.srv.world 

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Please read the Terms of Service at
https://letsencrypt.org/documents/LE-SA-v1.2-November-15-2017.pdf. You must
agree in order to register with the ACME server at
https://acme-v02.api.letsencrypt.org/directory
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# agree to the terms of use
(A)gree/(C)ancel: A

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Would you be willing to share your email address with the Electronic Frontier
Foundation, a founding partner of the Let's Encrypt project and the non-profit
organization that develops Certbot? We'd like to send you email about our work
encrypting the web, EFF news, campaigns, and ways to support digital freedom.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(Y)es/(N)o: Y
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for dlp.srv.world
Using the webroot path /var/www/html for all unmatched domains.
Waiting for verification...
Cleaning up challenges

IMPORTANT NOTES:
 - Congratulations! Your certificate and chain have been saved at:
   /etc/letsencrypt/live/dlp.srv.world/fullchain.pem
   Your key file has been saved at:
   /etc/letsencrypt/live/dlp.srv.world/privkey.pem
   Your cert will expire on 2021-03-17. To obtain a new or tweaked
   version of this certificate in the future, simply run certbot
   again. To non-interactively renew *all* of your certificates, run
   "certbot renew"
 - Your account credentials have been saved in your Certbot
   configuration directory at /etc/letsencrypt. You should make a
   secure backup of this folder now. This configuration directory will
   also contain certificates and private keys obtained by Certbot so
   making regular backups of this folder is ideal.
 - If you like Certbot, please consider supporting our work by:

   Donating to ISRG / Let's Encrypt:   https://letsencrypt.org/donate
   Donating to EFF:                    https://eff.org/donate-le

# success if [Congratulations] is shown
# certs are created under the [/etc/letsencrypt/live/(FQDN)/] directory

# cert.pem       ⇒ SSL Server cert(includes public-key)
# chain.pem      ⇒ intermediate certificate
# fullchain.pem  ⇒ combined file cert.pem and chain.pem
# privkey.pem    ⇒ private-key file
[4] If no Web Server is running on your working server, it's possbile to get certs with using Certbot's Web Server feature. Anyway, it needs that it's possible to access from the Internet to your working server on port 80 because of verification from Let's Encrypt.
# for the option [--standalone], use Certbot's Web Server feature

# -d [FQDN you'd like to get certs]

# FQDN (Fully Qualified Domain Name) : Hostname.Domainname
# if you'd like to get certs for more than 2 FQDNs, specify all like below

# ex : if get [srv.world] and [mail.srv.world] ⇒ -d srv.world -d mail.srv.world
[root@dlp ~]#
certbot certonly --standalone -d mail.srv.world

Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator standalone, Installer None
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for mail.srv.world
Waiting for verification...
Cleaning up challenges

IMPORTANT NOTES:
 - Congratulations! Your certificate and chain have been saved at:
   /etc/letsencrypt/live/mail.srv.world/fullchain.pem
   Your key file has been saved at:
   /etc/letsencrypt/live/mail.srv.world/privkey.pem
   Your cert will expire on 2021-03-17. To obtain a new or tweaked
   version of this certificate in the future, simply run certbot
   again. To non-interactively renew *all* of your certificates, run
   "certbot renew"
 - If you like Certbot, please consider supporting our work by:

   Donating to ISRG / Let's Encrypt:   https://letsencrypt.org/donate
   Donating to EFF:                    https://eff.org/donate-le
[5] For Updating existing certs, use [renew] subcommand.
To run [renew] subcommand, all certs which have less than 30 days expiration are updated.
If you'd like to update certs which has more than 30 days expiration, add [--force-renew] option.
However, [certbot] package from Snapd has systemd timer, so it does not need to run it manually anymore.
# systemd timer script is included in Snapd Certbot package

[root@dlp ~]#
systemctl status snap.certbot.renew.timer

*  snap.certbot.renew.timer - Timer renew for snap application certbot.renew
   Loaded: loaded (/etc/systemd/system/snap.certbot.renew.timer; enabled; vendo>
   Active: active (waiting) since Tue 2021-02-23 09:47:25 JST; 5min ago
  Trigger: Tue 2021-02-23 10:12:00 JST; 19min left

Feb 23 09:47:25 dlp.srv.world systemd[1]: Started Timer renew for snap applicat>

# [renew] is run 2 times every day like follows by default

[root@dlp ~]#
systemctl cat snap.certbot.renew.timer

# /etc/systemd/system/snap.certbot.renew.timer
[Unit]
# Auto-generated, DO NOT EDIT
Description=Timer renew for snap application certbot.renew
Requires=var-lib-snapd-snap-certbot-952.mount
After=var-lib-snapd-snap-certbot-952.mount
X-Snappy=yes

[Timer]
Unit=snap.certbot.renew.service
OnCalendar=*-*-* 10:12
OnCalendar=*-*-* 13:12

[Install]
WantedBy=timers.target

# for manual update, do like follows

[root@dlp ~]#
certbot renew

[6] If you'd like to convert certificates to PKCS12 (PFX) format for Windows, do like follows.
[root@dlp ~]#
openssl pkcs12 -export -in fullchain.pem -inkey privkey.pem -out dlp_for_iis.pfx

Enter Export Password:     # set any export password
Verifying - Enter Export Password:
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