def key=(*args)
      cert, passphrase = args.flatten
      ssl_context.key = OpenSSL::PKey::RSA.new(cert, passphrase)
    end
def key=(*args)
      cert, passphrase = args.flatten
      ssl_context.key = OpenSSL::PKey::RSA.new(cert, passphrase)
    end
Set to a PEM-format client private key