get_cert_chain.rb

=begin
Copyright (c) 2015 Red Hat inc
Permission is hereby granted, free of charge, to any person obtaining a copy
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in the Software without restriction, including without limitation the rights
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copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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THE SOFTWARE.
=end

require 'socket'
require 'openssl'

module Something
    # @param dst [String] the hostname or IP of SSL server
    # @param port [String, Integer] the port number to connect
    # @param hostname [String] hostname for using SNI connection
    # @return [Array] the certificate chain used by secure server;
    #   correct order is host cert first and then deeper down the chain.
    #   In reality though, admins do not always do the right thing
    #   (see https://utcc.utoronto.ca/~cks/space/blog/tech/SSLChainOrder).
    #   So I'm not sure whether the library always returns correct order here.
    def self.get_cert_chain(dst:, port:, hostname: nil)
      context = OpenSSL::SSL::SSLContext.new
      context.verify_mode = OpenSSL::SSL::VERIFY_NONE
      tcp_client = TCPSocket.new host, port.to_i
      ssl_client = OpenSSL::SSL::SSLSocket.new tcp_client, context
      ssl_client.hostname = hostname if hostname
      ssl_client.connect
      # ssl_client.peer_cert
      chain = ssl_client.peer_cert_chain
      ssl_client.close
      return chain
    end
end