Contribute to openssl/openssl development by creating an account on GitHub. Extract a certificate from a server. If it is to interact with the database, any decent client will do.psql can be called with the sslmode=require option. Making the HTTP request. Accessing the s_server via openssl s_client. openssl s_client -starttls smtp -connect example.com:25 openssl s_client -starttls smtp -connect example.com:465 openssl s_client -starttls smtp -connect example.com:587. $ openssl s_client -connect www.feistyduck.com:443 -servername www.feistyduck.com In order to specify the server name, OpenSSL needs to use a feature of the newer handshake format (the feature is called Server Name Indication [SNI]), and that will force it to abandon the old format. Don’t worry about this unless you need it because some application requires a PKCS12 file or you’re given one that you need to get stuff out of. TLS/SSL and crypto library. Think of it like a zip file for keys & certificates, which includes options to password protect etc. To view a complete list of s_client commands in the command line, enter openssl -?. Let's break this down into two parts. First, making the HTTP request, and second, extracting your content from the response. Hence in your test the openssl s_client command advertises that is supports NPN but the server turns a blind eye onto ot. SNI is a TLS extension that supports one host or IP address to serve multiple hostnames so that host and IP no longer have to be one to one. Convert a root certificate to a form that can be published on a web site for downloading by a browser. If the connection succeeds then an HTTP command can be given such as "GET /" to retrieve a web page. The handshake still passes OK because the extension appears to be non-essential (or at least considered to be such by openssl) and you get the connected TLS tunnel. A group of ciphers can also be passed. The hardest part here is that s_client closes the connection when its stdin gets closed. See man psql.. example. openssl s_client sni openssl s_client -connect example.com:443 -servername example.com. # openssl x509 -in cert.pem -out rootcert.crt. openssl s_client is not a particularly great tool for this, but it can be done. Use the -servername switch to enable SNI in s_client. # openssl s_client -connect server:443 -CAfile cert.pem. If it is to check the SSL certificate (which is why I came across your question), it still doesn't work with s_client as Magnus pointed out 7 years ago. To create a full circle, we’ll make sure our s_server is actually working by accessing it via openssl s_client: joris@beanie ~ $ openssl s_client -connect localhost:44330 CONNECTED(00000003) depth=0 C = NL, ST = Utrecht, L = Utrecht, O = Company, OU = Unit, CN = localhos t openssl s_client -connect ldap-host:636 -showcerts. 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