Você pode tentar algo assim:
$ echo 1 | \
openssl s_client -connect unix.stackexchange.com:443 \
-showcerts 2>/dev/null > /tmp/chained.pem && \
openssl crl2pkcs7 -nocrl -certfile /tmp/chained.pem | \
openssl pkcs7 -print_certs -text -noout