Extract certificate

extract_certificate.sh

#!/bin/bash
# Extract certificate from the target domain.
# Usage:
#   ./extract_certificate.sh {{domain name}} {{target port:default 443}}
# Example:
#   curl -L https://git.io/fp8Za | bash -s google.com
#   curl -L https://git.io/fp8Za | bash -s google.com 443

target=$1
port=${2:-443}

docker run --rm frapsoft/openssl s_client \
    -connect ${target}:${port} 2>/dev/null </dev/null \
    | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' \
    > ${target}.crt
ls -l ${target}.crt