Проверить срок годности SSL сертификата:

$ echo | openssl s_client -servername site.com -connect site.com:443 2>/dev/null | openssl x509 -noout -dates
notBefore=Mar 18 10:55:00 2017 GMT
notAfter=Jun 16 10:55:00 2017 GMT

Проверить кто выдал SSL сертификат:

$ echo | openssl s_client -servername site.com -connect site.com:443 2>/dev/null | openssl x509 -noout -issuer
issuer= /C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3

Проверить кому выдан SSL сертификат:

$ echo | openssl s_client -servername site.com -connect site.com:443 2>/dev/null | openssl x509 -noout -subject
subject= /CN=www.site.com

Всё вместе:

$ echo | openssl s_client -servername site.com -connect site.com:443 2>/dev/null | openssl x509 -noout -issuer -subject -dates
issuer= /C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3
subject= /CN=www.site.com
notBefore=Mar 18 10:55:00 2017 GMT
notAfter=Jun 16 10:55:00 2017 GMT

status 200

$ curl -Is http://www.site.com | head -1
HTTP/1.1 200 OK