Create a Let's Encrypt wilcard certificate

A wildcard certificate is useful to secure several services using different alias of the same domain name, in contrary to a certificate per alias. Let’s Encrypt offers now and freely such a service.

The creation of the wildcard certificate Let’s Encrypt is done by the CLI client certbot which needs to be installed on your distribution:

$ sudo apt install certbot

A working directory must be created to store generated files:

$ mkdir -p ~/certbot/{config,work,logs}
$ cd ~/certbot

To create a certificate, execute the following command given your domain name without any alias:

$ certbot certonly --config-dir config/ --work-dir work/ --logs-dir logs/ \
    --server https://acme-v02.api.letsencrypt.org/directory --manual \
    -d '*.monsite.fr'

The create process will ask you to add a record to your domain DNS zone. After this verification, the same command will need to be reused to regenerate the certificate before its expiration date.