openssl s client

openssl s_client -connect
   openssl s_client -connect example.com:443 -servername example.com
openssl s_client -showcerts 

• openssl s_client -showcerts -connect YOUR_DOMAIN.COM:443

• echo -n | openssl s_client -connect HOST:PORTNUMBER | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > /tmp/$SERVERNAME.cert

depth=0 C = XX, ST = YY, L = XXXXX, O = ORGA, OU = RND, CN = YOUR_DOMAIN.COM
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 C = XX, ST = YY, L = XXXXX, O = ORGA, OU = RND, CN = YOUR_DOMAIN.COM
verify error:num=21:unable to verify the first certificate
verify return:1
DONE

openssl s_client -servername <NAME> -connect <HOST:PORT> 2>/dev/null | openssl x509 -noout -dates

openssl s_client -connect

Activities

• How to check certification expiration date from command line: openssl s_client -servername ... | ... openssl x509 -noout -dates
• Download public certificate from a website: openssl s_client -connect

Related

• wget
• Traefik

See also

• openssl [ s_clients | -verify_return_error ]
• OpenSSL: RSA, ECDSA, WolfSSL, AES, Diffie-Hellman (DH) key-exchange, /etc/ssl/openssl.cnf, OpenSSL v3, openssl

https://serverfault.com/questions/139728/how-to-download-the-ssl-certificate-from-a-website