How to Build Custom Automated SSL Certificate Monitoring with Bash, Python, and Webhooks

Bash Script to Alert on Expirations Below 14 Days

#!/bin/bash
DOMAIN="example.com"
EXPIRY_DATE=$(echo | openssl s_client -servername "${DOMAIN}" -connect "${DOMAIN}:443" 2>/dev/null | openssl x509 -noout -enddate | cut -d= -f2)
EXPIRY_EPOCH=$(date -d "${EXPIRY_DATE}" +%s)
NOW_EPOCH=$(date +%s)
DAYS_LEFT=$(( (EXPIRY_EPOCH - NOW_EPOCH) / 86400 ))

echo "Domain: ${DOMAIN} has ${DAYS_LEFT} days remaining."

if [ "${DAYS_LEFT}" -lt 14 ]; then
    # Send alert to Slack Webhook
    curl -X POST -H 'Content-type: application/json' \
        --data "{\"text\":\"⚠️ CRITICAL: SSL certificate for ${DOMAIN} expires in ${DAYS_LEFT} days!\"}" \
        "${SLACK_WEBHOOK_URL}"
fi

The Smarter Alternative: Zero-Maintenance Passwordless Monitoring

Instead of maintaining self-hosted cron scripts that can fail if the monitoring box loses power or internet connectivity, you can use CheckSSLExpiry's free passwordless monitoring service.