init_ansible_ssh_host.sh

#!/bin/bash
#
# This script will get an SSH host certificate from our CA and add a weekly
# cron job to rotate the host certificate.
# 
# See https://smallstep.com/blog/diy-single-sign-on-for-ssh/ for full instructions

CA_URL="[Your CA's URL]"
ALLOWED_DOMAIN="[the domain name of accounts your users will use to sign to Google]"
CA_NAME="[A name for your CA]"

# Obtain your CA fingerprint by running this on your CA:
#   # step certificate fingerprint $(step path)/certs/root_ca.crt
CA_FINGERPRINT="[Your CA"s Fingerprint]"

STEPCLI_VERSION="0.14.6"

# curl -LO https://github.com/smallstep/cli/releases/download/v${STEPCLI_VERSION}/step-cli_${STEPCLI_VERSION}_amd64.deb
# dpkg -i step-cli_${STEPCLI_VERSION}_amd64.deb

# Configure `step` to connect to & trust our `step-ca`.
# Pull down the CA's root certificate so we can talk to it later with TLS
step ca bootstrap --ca-url $CA_URL \
                 --fingerprint $CA_FINGERPRINT

# Install the CA cert for validating user certificates (from /etc/step-ca/certs/ssh_user_key.pub` on the CA).
step ssh config --roots > $(step path)/certs/ssh_user_key.pub

# Ask the CA to exchange our host key for an SSH host certificate
TOKEN=$(step ca token vps432732 -host -ssh -provisioner=logs@horwood.biz -password-file=key)
step ssh certificate $HOSTNAME /etc/ssh/ssh_host_ecdsa_key.pub \
    --host --sign --provisioner "${CA_NAME}@${ALLOWED_DOMAIN}" \
    --principal $HOSTNAME --principal "" \
    --token ${TOKEN}

exit
# Configure and restart `sshd`
tee -a /etc/ssh/sshd_config > /dev/null <<EOF
# SSH CA Configuration

# This is the CA's public key, for authenticatin user certificates:
TrustedUserCAKeys $(step path)/certs/ssh_user_key.pub

# This is our host private key and certificate:
HostKey /etc/ssh/ssh_host_ecdsa_key
HostCertificate /etc/ssh/ssh_host_ecdsa_key-cert.pub
EOF

service ssh restart

# Now add a weekly cron script to rotate our host certificate.
cat <<EOF > /etc/cron.weekly/rotate-ssh-certificate
#!/bin/sh

export STEPPATH=/root/.step

cd /etc/ssh && step ssh renew ssh_host_ecdsa_key-cert.pub ssh_host_ecdsa_key --force 2> /dev/null

exit 0
EOF

chmod 755 /etc/cron.weekly/rotate-ssh-certificate