openssl: add subcommand pages (#4886)

pages/common/openssl-s_client.md

@@ -0,0 +1,16 @@
+# openssl s_client
+
+> OpenSSL command to create TLS client connections.
+> More information: <https://www.openssl.org/docs/manmaster/man1/openssl-s_client.html>.
+
+- Display the start and expiry dates for a domain's certificate:
+
+`openssl s_client -connect {{host}}:{{port}} 2>/dev/null | openssl x509 -noout -dates`
+
+- Display the certificate presented by an SSL/TLS server:
+
+`openssl s_client -connect {{host}}:{{port}} </dev/null`
+
+- Display the complete certificate chain of an HTTPS server:
+
+`openssl s_client -connect {{host}}:443 -showcerts </dev/null`