openssl-s_client:tldr:04296

The openssl s_client -connect ${host}:${port} -servername ${hostname} command is a way to use the OpenSSL library to establish a secure connection to a specified server.

Here's a breakdown of the command and its parameters:

• openssl: This is the command to run the openssl program, which is a command-line tool for using the OpenSSL library.
• s_client: This is a subcommand of openssl that specifically deals with SSL/TLS connections from a client perspective.
• -connect ${host}:${port}: This specifies the host IP address or domain name and the port number to establish the connection with. ${host} and ${port} should be replaced with the actual values.
• -servername ${hostname}: This parameter specifies the hostname to be sent as the SNI (Server Name Indication) extension in the ClientHello message. ${hostname} should be replaced with the actual value.

Basically, this command is used to test and interact with SSL/TLS servers from the client-side using OpenSSL. It establishes a secure connection to the server specified by ${host} and ${port}, sending the ${hostname} as the Server Name Indication.