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| #!/bin/bash | |
| # | |
| # This script will get an SSH host certificate from our CA and add a weekly | |
| # cron job to rotate the host certificate. | |
| CA_URL="[Your CA's URL]" | |
| # Obtain your CA fingerprint by running this on your CA: | |
| # # step certificate fingerprint $(step path)/certs/root_ca.crt | |
| CA_FINGERPRINT="[Your CA"s Fingerprint]" | |
| STEPCLI_VERSION="0.14.0-rc.4" | |
| curl -LO https://github.com/smallstep/cli/releases/download/v${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 > $(step path)/certs/ssh_user_key.pub | |
| # Get an SSH host certificate | |
| HOSTNAME="$(curl -s http://169.254.169.254/latest/meta-data/public-hostname)" | |
| LOCAL_HOSTNAME="$(curl -s http://169.254.169.254/latest/meta-data/local-hostname)" | |
| # This helps us avoid a potential race condition / clock skew issue | |
| # "x509: certificate has expired or is not yet valid: current time 2020-04-01T17:52:51Z is before 2020-04-01T17:52:52Z" | |
| sleep 1 | |
| # The TOKEN is a JWT with the instance identity document and signature embedded in it. | |
| TOKEN=$(step ca token $HOSTNAME --ssh --host --provisioner "Amazon Web Services") | |
| # To inspect $TOKEN, run | |
| # $ echo $TOKEN | step crypto jwt inspect --insecure | |
| # | |
| # To inspect the Instance Identity Document embedded in the token, run | |
| # $ echo $TOKEN | step crypto jwt inspect --insecure | jq -r ".payload.amazon.document" | base64 -d | |
| # Ask the CA to exchange our instance token for an SSH host certificate | |
| step ssh certificate $HOSTNAME /etc/ssh/ssh_host_ecdsa_key.pub \ | |
| --host --sign --provisioner "Amazon Web Services" \ | |
| --principal $HOSTNAME --principal $LOCAL_HOSTNAME \ | |
| --token $TOKEN | |
| # 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 |
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