cert_pinning.rb

 # The value of ssl_verify_callback is assigned to Net::HTTP#verify_callback
  response = RestClient::Resource.new(
    'https://localhost?q=Foo',
    :ssl_client_cert => OpenSSL::X509::Certificate.new(File.read(ssl_client_cert)), # Part of the Client Certificate Validation
    :ssl_client_key => OpenSSL::PKey::RSA.new(File.read(ssl_client_key), key_pass), # Part of the Client Certificate Validation
    :ssl_ca_file => ssl_ca_file, # Part of the Client Certificate Validation
    :verify_ssl => OpenSSL::SSL::VERIFY_PEER, # Part of the Client Certificate Validation
    :ssl_verify_callback => lambda(&method(:ssl_verify_callback)) # Part of the Client Certificate Validation
  ).get